rRootage is an abstract shooter, created by Kenta Cho and ported to Linux by Evil Mr Henry.

Screenshot:

Download
Sourceforge page
Debian distro: apt-get install rrootage
Foresight Linux or Specifix Linux distros: conary update rRootage

Also try:
Noiz2sa
A7Xpg
Tumiki Fighters
Parsec47