Protoship 2 is a Shump (Touhou, Gradius, R-Type) that is different from others in that the enemy waves before the boss are random. This makes it so that you have to relay on reflexes rather than memory. Protoship 2 also offers some very nice power-ups in the form of double shot lasers, misses, a shock-wave that can cut through many enemies at once, and a screen obliterating bomb. Protoship 2 has three differant difficulties, so even those who are not normally good at Shmups can have fun with this, and also includes full-screen support, multiple profiles, and can run on any OS with Java installed.
Download