Barbs are Required to be illiterate, unless they waste extra skill points (which they have precious few of compare dot other classes) on it.
Barb and Bard both are restricted from any lawful alignment, and are restricted from levelling up if they drift into a lawful alignment (this is true of any other alignment restriction mentioned).
Clerics are alignment restricted based on their deity, and domain restricted based on their alignment... although in this particular case I will make note that, contrary to what many seem to say, clerics in 3.5 were not actually required to worship a specific deity at all, and if they did not could pick their alignment freely... and amusingly, if you didn't worship a particular god, there was no lock-out for drifting, so a non-deity cleric would never go ex-cleric.
Druids were locked to at least one Neutral axis point - could be either, but they had to maintain at least one.
Monks had to be lawful, Paladins had to be Lawful Good
Wizards could only choose to specialise in particular school if they accepted being hard locked out of two other schools of magic (My brain is saying there's something kooky with divination though... like it got preferential treatment for some arbitrary and unjustified reason... like, only locked out one school, and could not, itself, be locked out...)
You were soft-restricted in multiclassing by favoured classes based on race – if you were, say, a level 15 halfling fighter, you couldn't multiclass into ranger without having to take a heavy XP penalty... because halflings favoured rogue. Everyone but Human, I think, had a favoured class, which meant that everyone but human would take an xp penalty for multiclassing if they didn't pick their racial favourite class, or start with it (there's more to the rule than that, but I'm being brief).
You were restricted on what languages you could learn or know, based on your race; You're a halfling, so it doesn't matter that you grew up in the stacks of Candlekeep, have an 18 Int at level 1 and are setting out to see the world as a Bard, knower of stories in dozens of dialects... you CANNOT know Draconic, Sylvan, Giant and Infernal as your bonus languages... you just can't, full stop... nope, you're a halfling so your bonus languages are: Dwarven, Elven, Gnomish, Goblin, and Orc. Fun.
A whole bunch of skill were only allowed to be attempted at all if you had put ranks in them... and there were skills in place the required checking for many minute and discrete things to the extent that you couldn't possibly afford to spend points in all of them... So good luck to your 9 strength elven dex fighter, who, because they didn't want to waste skill ranks specifically on the 'swim' skill, because they only had so many points to spend, and needed to put them into actually combat-relative ones like tumble... now has to accept the fact that they will drown if they are dropped in the middle of a calm, placid lake on a sunny, still day, because they still have to check to swim out, and their take-10 is a failure.
