These components could equally well be called "miscellaneous tweaks".
"If you're in the woods, and you run into an angry bear, don't worry about it. Bears can't move very fast, you can outdistance it at a brisk walk".
It's unrealistic that BG bears can't catch up with the party. This component tweaks their movement rate (when hostile) until it's about the same as for humans. This also makes the druid's bear shapeshift less annoying.
Grant large, flying, non-solid or similar creatures immunity to Web and Entangle
Logically, things like Fire Elementals, Grey Oozes, and Giants ought to be unaffected by Web and Entangle effects. This component grants them immunity to those effects. Affected creatures are Elementals (all except small Earth), djinnis, efreetis, anything larger and stronger than an ogre (which basically means umber hulks, shambling mounds, large demons, giants, otyughs, and wyverns), magical flying swords, and oozes and slimes.
More realistic wolves and dogs (BGEE,TUTU,BGT)
In the real world, wolves rather rarely attack humans; indeed, they normally keep their distance. In the Sword Coast, though, wolves are apparently ruthless, fearless predators that think nothing of attacking even large parties of heavily armed adventurers. (And, as a corollary, even wilderness-oriented types like rangers and druids spend much of their time fighting off attacks from implacable wolf packs.)
This component makes the behaviour of wolves (and also wild dogs) a bit more realistic. They won't usually attack humans (they still do sometimes: it's been a harsh winter and game is scarce). They'll generally retreat if more than a few of them are injured or killed. If you approach them, they might take a bite out of you, but just as likely, they'll keep their distance.
This component has no effect on non-"normal" wolves (dire wolves, winter wolves and the like), since for all I know, they really are ruthless predators. Its main point is to spare the author (who rather likes wolves) the heartache of perpetually having to cut them down and listen to the rather sad yelp they make when you kill them.
This component (inspired in part by Wesley Weimer's Shapeshifter Rebalancing component) modifies all of the druid innate shapeshift abilities (and the druid/cleric elemental-shapeshift HLA) to be useable instantly (that is, without requiring a six-second cooldown before the next spell can be cast). It does so by creating "symbolic paws": if you equip one, you instantly shapeshift. Other than that, the effects of the shapeshift are largely the same as previously, though some of the ability score and attack bonuses have been tweaked slightly. Note that shapeshifting still blocks spellcasting.
If you have both this component and the "improved priests" component installed, enemy druids will use improved shapeshifting.
Make party members less likely to die irreversibly
This component tries to prevent "chunking", the annoying permanent death of your character when you're reduced below -10 hp. Characters who get reduced to 0 hp or below just die in the usual fashion and can be resurrected. It isn't possible to prevent quite all forms of chunking (massive damage from fire, in particular, still seems to cause chunking fairly reliably), but this component should make it a rarer occurrence. This may be useful in the later stages of the game, when melee opponents often do 30-40 hp damage per blow - that 10 hp safety margin starts to feel slender.
Reduced reputation increase
In general, if you're playing a half-way honorable character in BG2, your reputation fairly rapidly reaches 20 and stays there. The idea of this component is to slow down the rate at which you gain reputation: you can choose the degree of slowdown.
In more detail: any time you would have gained 2 or more reputation points, you gain one fewer point than you should have. Any time you would have gained one, it's decided at random whether you actually do gain it, according to the probability you choose at install time.
Allow player to choose BG1 NPC proficiencies and skills (TUTU,BGT)
At the moment the various NPCs who join your party have their existing proficiencies, thief skills etc. determined for you according to what the designers of BG and/or Tutu had in mind. There's nothing wrong with this, but it can be interesting - especially if you've played several times - to have more flexibility.
This component gives you the chance to select each character's proficiencies from scratch. It does so in a slightly convoluted way (to get around game-engine difficulties): when a new NPC joins your party, they start at level 0. They immediately go up a level, so you get to choose their starting skills. As soon as you've levelled them, they gain enough experience to go up to about the level of the PC, and you can give them any remaining proficiencies.
This differs from the BG2 Tweaks version (which is overwritten) because you get to choose proficiencies even for 1st-level characters. The component only works for the "core" NPCs in BG, not for any NPCs added by someone else's mod (or for BG2 NPCs). It won't work for a given NPC if you install it after you've already entered their area.
Note that at present this component is not available for the Enhanced Edition of Baldur's Gate. (I haven't yet found the time to get my head around how BGEE handles NPCs.)
Note: The patch takes a few seconds to come into effect. If there's a 3-4 second pause when your character's statistics (hit points, say) aren't right, don't worry about it.
Warning: Occasionally this component seems to give odd results for people; be warned. (Trying to mess around with them during the above 3-4 second pause seems to be the reason.) There is a much more stable and powerful version of this mod due to Nythrun available at the Gibberlings Three site; however, that version cannot be used during an ongoing game.)
Allow BG1 NPC pairs to separate (BGEE,TUTU,BGT)
One of the more frustrating aspects of BG is that many of the more interesting NPCs come in inseparable pairs (Khalid and Jaheira, Minsc and Dynaheir, etc.) Of course, it's always possible to get round this by leaving one member of a pair in a building or getting them killed, but it does spoil the suspension of disbelief a bit.
This component allows you to separate the pairs. If you kick one member of a pair out of the party, then the other still leaves - but if you speak to one member of a pair and invite them to join up, you get a dialogue option to take them but not their partner.
BG1 NPCs go to inns (BGEE,TUTU,BGT)
One of the nice features of BG2 is the ability to ask NPCs to meet you somewhere else, rather than just getting them to stand around forlornly. This component introduces this feature for the "core" BG NPCs. You can send them to the Friendly Arm inn, the Elfsong tavern in Baldur's Gate (from chapter 5), the Nashkel Inn (if you've been to Nashkel), or the Jovial Juggler in Beregost (if you've been to Beregost). You can't send them there from Balduran's Isle, the Ice Island, the Candlekeep dungeons, or the lower levels of Durlag's Tower..
To send someone to an inn, first kick them out of the party. Then talk to them - you should be given the opportunity to ask them to go to an inn and await you there.
This component isn't compatible with the similarly-named BG1 NPC component "NPCs wait at inns". Install whichever one you want (you won't be allowed to install more than one). There isn't much difference between the two - the dialogue is handled a bit differently, and this version lets you send people to more inns.
Move BG1 NPCs to more convenient locations (BGEE,TUTU,BGT)
Many of the BG NPCs are inconveniently located - either at places where you can't get to at all until late in the game (e.g. Baldur's Gate, the Cloakwood), or places where you in principle could get to but realistically wouldn't. This makes it annoying to experiment with varying your party: you have to leave extended gaps in your party until quite late, or unrealistically sneak into later-game areas to act on your Reload Knowledge of where someone is.
This component moves as many as possible of the NPCs to locations where you are likely to run into them fairly early in the game. Obviously it doesn't move all by any means (many have plot-related reasons for their locations).
See here for details of who has been moved and to where. Note that this component will only work if you start a new game.
BG1 NPC also moves some NPCs. If you've got BG1 NPC installed, this component will only move those NPCs (Shar-Teel and Viconia) whom BG1 NPC leaves alone.
Allow Yeslick to use axes (BGEE,TUTU,BGT)
It seems appropriate that Yeslick, who is a dwarven fighter-cleric, ought to be able to use the traditional dwarven weapon; this component allows him to.
(There is a loophole here: due to the way the game engine works, this actually allows all fighter-clerics (not just Yeslick) to use axes. Yeslick is actually the only NPC fighter-cleric in the core game but it might affect third-party NPCs, or your primary character (and, for BGT users, it will affect Anomen). If you want to take advantage of this then be my guest, but it wasn't the intended function of the component.)
Skip the Candlekeep tutorial sections (BGEE,TUTU,BGT)
The Prologue to BG is a perfectly good tutorial in the Infinity Engine for complete beginners. By the time you return to it for the Nth time, it's unutterably tedious - but you more-or-less have to do it, because even the small amount of gold and XP it gives you is pretty vital for later. It doesn't really even add colour, because realism is always being spoiled by these damn monks telling you which button to press.
This component gives you two ways around this problem.The first option (which leaves the tedium unchanged but resotres the verisimilitude) just removes the green-robed monks. The less-than-serious alternative choice, inspired by PPG's Dungeon-Be-Gone, lets you skip the whole thing: at the start of the adventure, a guard will come up to you and give you the chance to collect all the cash and XP from him. He'll give you a decent interval to shop, and then teleport you direct to Gorion ready for the start-of-game ambush.
Be warned that the dialogue with the guard is unrealistic and written for laughs. Realism is restored once you start talking to Imoen and Gorion.
Allow the Cowled Wizards to detect spellcasting in most indoor, above-ground areas in Athkatla (BG2,BG2EE,BGT)
The Cowled Wizards claim to ban magic everywhere in Athkatla; in practice, though, they only complain if you cast spells out of doors. This component extends their watch to most indoor, above-ground areas in Athkatla (there are a few exceptions, mostly places where wizards live (e.g. Prebek's tower) or where it's likely that the owners have made arrangements with the Cowled Wizards (e.g. the Copper Coronet).
Increase the price of a licence to practice magic in Athkatla (BG2,BG2EE,BGT)
The default price for a magic licence from the Cowled Wizards is 5,000gp. This component allows you to increase it to an amount between 10,000gp and 50,000gp, depending on which option you choose during installation.
Increase the price asked by Gaelan Baele (BG2,BG2EE,BGT)
This component aims both to make it more realistic for the player to linger in chapter 2 of SoA (which in gameplay terms is often rather tempting, but is hard to justify on roleplaying grounds) and to add an extra challenge by restricting the player's wealth in the first part of the game. As everyone knows, in the unmodded game Gaelan asks the player to provide 20,000gp. With this component installed, he will want more - between 40,000gp and 120,000gp, depending on which option you choose during installation.
Make Freedom scrolls available earlier (BG2,BG2EE,BGT)Scrolls of Freedom (the spell that reverses Imprisonment) are fairly thin on the ground early in SoA, whereas Liches love Imprisoning people. This component makes a few scrolls of Freedom available from Athkatlan stores (the Coppor Coronet and the Adventurer's Mart, in fact.)
Make Watchers' Keep accessible between SoA and ToB (BG2,BGT)
In roleplaying terms, the natural time to explore Watchers' Keep is between the end of Shadows of Amn and the start of Throne of Bhaal. Before chapter 4 you're probably too weak; in chapters 6 and 7 of SoA you're in a desperate race against time; in ToB, the way the start works makes it difficult not to take random time off from urgent business to explore Watchers' Keep.
This component moves the start location of Throne of Bhaal to Watchers' Keep, so that you're moved there immediately after the end of SoA. You can then explore WK to your heart's content. When you want to start ToB, just leave WK via the world map. You can still return to WK after leaving.
Be warned: you don't have any stable base, or any way to change your party, as long as you're starting at WK. If you find you need either, you'll need to do the first part of ToB. Similarly, although you could start a new game of ToB using this component, this is only a good idea if you're masochistic enough to want to solo Watchers' Keep with a starting-level ToB character!
This component is only available on Windows versions of SCS, and isn't at present available on BG2EE.
Warning: If you install this component you will not be able to access Watcher's Keep during the Shadows of Amn part of the game. This is to prevent a persistent bug, which I've been unable to track down, whereby going to WK during SoA triggers the chapter counter to advance to chapter 8.
Recover lost items from Hell (BG2,BG2EE,BGT)
Because you're transported directly from Hell at the end of chapter 7, any items on the ground (notably, those dropped by slaughtered companions) are lost in the lower planes. This component (suggested by the bigg) fixes this problem: your items will be on the ground waiting for you when you start chapter 8. The component is compatible with the "Make Watchers Keep accessible between SoA and ToB" component, and you can install them in either order.
Randomize the maze in Watcher's Keep (BG2,BG2EE,BGT)
This component is for the benefit of people who've now basically got the Watcher's Keep teleport maze memorized. It randomly rearranges the maze to one of three different alternative configurations. Don't install or reinstall this component while you're exploring the maze (before you enter it, or after you've left it, will be fine).
Remove unrealistically helpful items from certain areas (BG2,BG2EE,BGT)
Vampires do not stockpile stakes in their lairs; magic golems are not usually found near stashes of nonmagical weapons; demons' lairs are not usually stocked with books explaining how to eliminate their defences and wands stocked with the requisite spells; trolls are not generally found in places filled with fire and acid arrows; cities under siege do not generally have large quantities of +3 weapons for sale in bars. But in BG2 all these things occur. Presumably this is intended to reduce frustration, but I just find it spoils my suspension of disbelief. This component tries to remove all such implausibly-placed items. (Obviously, things like stakes and fire arrows are still plentifully available, but you can't count on just finding them lying around where you want them.)
Remove unrealistically convenient ammunition from the game (BG2,BG2EE,BGT)Similarly, the game has vast stashes of ammunition lying around for the taking, presumably because the developers thought you'd be bored of having to buy it. This component removes all the ammunition from containers, for those who find things just a bit too convenient to be realistic.
This component can be fine-tuned. You can choose to remove only the non-magical ammunition, to remove all the ammunition except those nice +3/+4 items you find in Throne of Bhaal, or just to remove everything.
Delay the arrival of the "bonus merchants" in the Adventurers' Mart and the Copper Coronet (BG2,BG2EE,BGT)
This component causes the "bonus merchants" (Deidre and Joluv) to appear a little later in the game (by default they are in the Adventurers' Mart and the Copper Coronet, respectively, as soon as you go there). One of them (chosen at random) will appear once you've started Chapter Six; the other will appear once you've either completed four of the "stronghold quests" or recovered the Rhyn Lanthorn.
You don't need to have the bonus merchants already installed (e.g. through Tweak Pack) to run this component; if you do, it won't matter.
Treat mages' and priests' High-Level Abilities as innate abilities rather than memorisable spells (BG2,BG2EE,BGT)
This component causes the 10th level spells that mages get as High-Level Abilities, and the Quest spells that priests get likewise, to become disentangled from existing 9th level mage spells and 7th level priest spells. If installed, 10th level and Quest spells are no longer added to the character's list of spells to learn. Instead, each can be cast once per day in addition to the character's normal spells. Each spell can only be taken once. Note that clones (Projected Images and Simulacra) of the spellcaster do not get High-level abilities.
The component should be compatible with other mods (notably Refinements) which change the High-Level Ability system. If it is installed, SCS mages and priests will also receive High-Level Abilities in this way.
I'm grateful to TheBigg and Vilcakis, from whose rather similar mod I took significant inspiration, and to Ardanis for the suggestion that each ability should only be available once, which changed me from a strong opponent of this change to a (cautious) supporter.