Do you know any other game with six degree of freedom and no gravity?

There aren't any worth mentioning. Shattered Horizons was similar but it's dead.

Independance War 2 here on GOG is. It's a different style of game, but you have 6DOF :)

Forsaken. It is an awesome game that will hopefully come to GOG eventually. It is basically a straight up Descent clone but you fly "bikes" in a post apocalyptic world. The single player is good, though it does spawn enemies behind you and such, but the multiplayer is loads of fun. There is a source port here:
http://fly.thruhere.net/#projectx

Miner Wars is sort of a Descent/Freespace/MMORPG game which is coming out. I played with the alpha a bit. You could literally create your own tunnels through asteroids but could also fly around in the surrounding space as well.

There was another game called Radix: Beyond the Void released around the same time as Descent. Sort of a Descent/Doom hybrid. Didn't have full degrees of freedom as in Descent, basically your ship couldn't roll but could pitch up and down say around 40 degrees from horizontal and the ship would always be moving forward though you could go faster when desired. The maps were also planer with a few minor exceptions. Not as good as Descent, but fun nonetheless.

http://www.youtube.com/watch?v=XpPmhtBRCbc
Radix looks like loads of fun! Basically a 2.5D Descent, or Doom with jetpack.... Will buy if it's on GOG ;)

Terminal Velocity has some tunnel flying, but you can't strafe and it only flies forward. It has more surface fighting than tunnel fighting though.

Yeah, I would argue that Terminal Velocity (and Fury3) aren't quite similar enough to cut it. Fun games, but the character of the game play is just quite different. I think I'd put AquaNox in that category as well.

Forsaken was the closest thing to Descent. But it wasn't that good. Nothing beats Descent.

I thought Forsaken's controls and multiplayer were quite excellent actually. The ship control felt tighter and multiplayer was a blast!

Miner Wars

It's in alpha right now, but it is somewhat playable. There is a demo which gives you access to the game except for one thing - you can't save. It's $20 one-time purchase for the singleplayer game OR the MMO ($40 for both). Alpha really is alpha, so there will be a bunch of placeholder sounds and buttons. There is some fighting out in the open, but most of the fighting are either in asteroids where you can dig your way through, or in small bases. And it's the type where you no matter how good your spatial awareness is, you eventually won't know what is the floor and what is the ceiling.

Retrovirus is a new game just coming out. (And it may *possibly* be released here on GOG! :)

FORSAKEN was a really good game too. If you liked DESCENT, you would like FORSAKEN.

Has anyone actually tried that sourceport someone linked a few posts earlier? I've never really had trouble getting Forsaken to run vanilla, even on 7, so kinda curious.

Nope! sorry, i didnt played Forsaken in a looooong time.