Game: Dead Cyborg
Episode 1 already released for windows, Linux version should be released soon too.
Note about development model:
[quote]The game will be published by episodes (2-3 hours of play per episode). The first episode is released. The next episode will come when enough donation is paid for the first episode. The full game will have 3 episodes.[/quote]
So, if you like it - donate.
Well, I think you'll need to draw a line between open source and freeware, and don't forget paragraph 2 and 3 which is in conflict with your imagination.
Game: Cave Story
Awesome game, though very difficult. It has great storyline with three endings (got the "normal" one, but without Curly; not sure if I'll be able to get "extended" one, may be too difficult for me), various weapons (you can't collect all of them at a time - at some points you should decide which weapon to choose), secrets, lots of different enemies, etc. If you like old-school platform games this is definitely one to try.
I think that NC does not restrict free non-commercial redistribution. Just imagine the fat dude, that sells free opensource game, which he did`t made! I think that if the Ur-Quan community wanted to sell it, they would choose other license.
This is a BRILLIANT game, one of the best ever created. Definitely. 10 stars, no doubt. I've played it ~3 years ago (it was then known under the name of Hammerfall) on windoze, and it just had blown my mind. Awesome story, awesome graphics, awesome gameplay. Nothing to complain about (well, maybe only the english translation was not perfect then, but things might had changed during these 3 years). Seriously, you must try it.
Just in case you don't know: you can already preorder game here