Notch made a zombie game, and you can play it free now.

Minecraft creator Notch participated in a first-person shooter game jam, and he had to put something together in seven days, and what came out of that is a Unity-powered arcade-style zombie arena called Shambles in which the mouse sensitivity is too low. There's no objective; just run around killing for points and to collect health and ammo drops while trying not to die. Note: there is no auto-reload here.

Thanks, Eurogamer.