Well, here's my try at a Defender-ish game... (Score 1)

http://wordwarvi.sourceforge.net/ It's at the moment, linux, Mac OS X, and FreeBSD only. Uses portaudio, and gtk mostly, so it should be not too hard to port to Windows if somebody wants to attempt it. It also supports the xbox 360 controller with working rumble effect on linux, so far as I know, the first game on linux to do so (though I might be wrong about that.) A lot of people seem to like it so far. You do need portaudio v. 19, not v. 18. It will compile without audio support, however, you are missing *a lot* if you do that.