True 20 is a greatly streamlined d20 game for fantasy, modern and sci-fi.
It keeps many things that make d20 what it is, including classes, levels and skills, but is greatly streamlined. There are only three classes: Warrior, Expert and Adept. Classes get a set number of skills, but you can choose any class skills for them that you want.
Class abilities become feats, and every class gets 4 feats at 1st level, and one feat every level after that.
Most feats are general, but each class does have a small, specific feat selection all its own, to give the classes some unique flavor. You also get a special ability from the class you take at first level, and this is only available to those who take that class for their first class.
There are also fewer skills, with skills folded in together. Hide and Move Silently become Stealth, Balance and Tumble become Acrobatics and so on.
It also does away with HP, replacing them with the M&M damage save.
Magic is handled as feats, available only to Adepts.
The game also has equipment for fantasy, modern and sci-fi games, and four campaign models.