Ichor

Ichor is a shoot-em-up without any bullets -- instead, your movements push around a viscous fluid which, should they touch it, liberates your comrades into nirvana. Meanwhile you have to navigate and avoid their fluid (until the cycle of suffering that is life is too much for you). A very simple concept with surprisingly deep game dynamics, which all come from the physics of fluid dynamics. Learn to play in the flow: follow where it leads and subtly manipulate it toward success; resist it and you are doomed.