There are other "d20 system" games - e.g. I remember the Babylon 5 RPG uses it.
I've reached the conclusion it's a bad idea though. The more generic a system it is, the less appropriate to the specific game it can be, and vice versa. So I much prefer systems that are very dedicated to their particular game experience. E.g. I absolutely love The Mountain Witch, which is a game that feels like a samurai movie, and everything in the system supports that: there's a special mechanic for duels, another for betrayals, all conflicts interact with your personal history/issues...
I've reached the conclusion it's a bad idea though. The more generic a system it is, the less appropriate to the specific game it can be, and vice versa. So I much prefer systems that are very dedicated to their particular game experience. E.g. I absolutely love The Mountain Witch, which is a game that feels like a samurai movie, and everything in the system supports that: there's a special mechanic for duels, another for betrayals, all conflicts interact with your personal history/issues...