Akasa

Akasa is a spaceship game in the style of Xevious. You fly along a path using lasers and bombs to destroy enemies in the air and on the ground respectively. The goal of the game is to destroy the nuclear warheads at the end of each level. To accomplish this you must destroy the power cubes in each level to weaken the warhead's shield wall. Akasa is slightly different from other games like it in that you can turn around and you have limited ammo for your primary weapon. The game features an online leaderboard, which is still being maintained by the dev even though the last update to the game was in 2007.

My opinion: Akasa is a pretty good game for it's genre, although I am terrible at it. I think some people who like games like this may be turned off by how to move backwards you actually have to turn around, since the turning animation isn't instant so you can't immediately move backwards if you need to. It does have a cool mechanic where you can detonate bombs by firing your laser, which is quite fun to do. The graphics are a little outdated, but that's forgivable seeing as this is a freeware game from around 2005. The font for the menus is awful though.

Akasa is by David De Candia and is open source. You can find it here. Also, the rest of this guy's website is kinda interesting in a weird tech/zen sorta way.