yes but how exactly do you make your mod run from it own engine? I'm kind of confused on how they manage that
It still "runs" from the same "engine", more or less. It's just that now it's cool to use that engine, without using the game that it was designed to drive. So they haven't taken the engine away (in fact, they really just took the other game away). It's just that you no longer need to also have Quake 3 installed for it to work. You may want to look up "open source" in your own language. Take a look at the following four definitions, and then do a little research about Quake.
Also, it may be easier for you to think of it like this. Say you buy a car because you really like the engine (maybe it's an old 327 or something). But you hate the body. So you tear off the body, and chop the frame, and completely modify the vehicle until it looks completely different. Now when you drive it down the street, nobody can recognize it. But still, the same engine is making it go, with minor changes, while, appearance-wise, it is a radically different-looking thing. A somewhat oversimplified analogy, but I hope it helps.
Cheers!
ioquake3Open sourceSource codeHuman-readableP.S. Tremulous doesn't really have it's "own" engine. It's just that id software made it cool to make a game using the Quake 3 engine without also having to install the game of Q3a. It's not standalone from the engine, so much as it is standalone from the game the engine was originally made for.

P.P.S. I highly recommend Google & wikipedia. While not the be-all and end-all of information resources, they are both quite useful for at least getting a general background on any particular subject.

P.P.S.S. And take any advice about deleting system folders with due skepticism.
