It's freeware, but, it's pretty fun.
It basically goes like this:
Instead of having lives, you have a timer.
There's no powerups, but you can change the direction and spread of your weapon.
There's a boss, every stage. And just the boss itself, nothing else.
Depending on which part of the boss you destroy first, that same part will become harder to destroy in the next stage.
If you die, you lose 20 seconds off the clock, as well as whatever weapon you were killed by will become more used in the next stage.
It's pretty fun, doods. I recommend it, as well as the other games on the site.