Erudite
The Erudite (knowing a lot) is a psionic class in 3.5e Dungeons & Dragons. It is also one of six most powerful classes in all of 3.5e, but not as it appears in the main book. In practice it is the the Wizard to the Psion's Sorcerer, with a bit of Archivist thrown in. The Erudite is something of an unknown class, being muffled away all the way in the back of Complete Psionics alongside the Epic rules for psionic characters.
How to use it
The Erudite works very much like a regular Psion: it has power points, uses them to cast its psionic powers, can interact with psicrystals and yadda yadda yadda. Its BAB is only so-so (10/5), has 6/6/12 at saves at level 20 and only d4 hit die. It has only limited skills and gains bonus psionic feats at levels 1, 5, 10, 15 and 20. The Erudite can oalso use only a limited amount of unique powers to day: meaning that while at first it can only cast a single level 1 power twice on a day, this later means that it can use up to 11 different powers per day. The main difference between it and the Psion is that the Psion learns powers on its own accord, while the Erudite has to learn them from somewhere: either from an item containing this power or from someone who knows such a power. The target has to be willing to do so: meaning that if you want to learn from someone you must either talk them into it, use some kind of spell to make them do it or knock them out (because unconscious psions can't say no).
When the Erudite pulls such a power from a source (which requires two Psicraft checks on DC 15 + power level if the source of the powers fails a Will save DC 13 + Erudite Int bonus) he can either use it immediately but only once, OR he can meditate on the power for 8 hours and add it permanently to its repetoire. Such power comes at a price however... at 20xp per power learned per Erudite level. While this is something of a notable commitment for a lower level character, at the higher levels this becomes almost free. This means that learning single powers will work, but you can't pilfer an enemy's mind completely empty if you don't stick around their unconscious body for a few days. And while this does not damage the minds of anyone you take the power from, items containing the spell will lose it.
How to break it
Now, while this would be pretty useful on its own, in 2007 a web expansion was released regarding the Erudite. This gave birth to the Spell to Power variant of the Erudite, which allows them to do the power learning thing with arcane spells. This means that a Erudite cannot only learn psionic powers, but also ALL Wizard, Bard and Wu jen spells and use them as power. The sheer diversity that comes with such a repertoire makes the Erudite diverse without peer. Even better is that if you manage to learn a spell at a somewhat low level, you can still cast it if you have enough PP. First-level spells cost 1 PP each with +2 per spell level, meaning that if you spend all 17 of your PP you can cast level 9 spells at 4, so slapping your overleveled BBEG with Energy Drain and killing him on the spot is very much a possibility. Or at least that's what could happen if there wasn't a limit equal to your manifester level on how many power points you can use on a power.
Now, casting your spells is always done at the minimal level when dealing with "X damage per caster level", but for every point you spend this goes up by 1. This can be costly if you try to go for max damage spells, so keep this in mind. You can also choose to pay 2 points extra to pay for ANY material costs that come with the spell, so if you want to have some fun with Fabricate, knock yourself out.