Endless Sky is a sandbox-style space exploration game
FlightGear Flight Simulator: free open-source multiplatform flight sim
Skyscrapersim Abandoned
Legandary Story of the Zarakite
A planetarium software that shows a 3D simulation of the night sky
A cross-platform interpreter for many point-and-click adventure games
A space race game in the style of A Dark Room
Minecraft clone written in C using modern OpenGL
Dodging shapes just got serious
A MMORPG Engine, written in PhP and SQL
Make star maps for anywhere at anytime
Get those letters!
Scrolling + Skating + Spikes = Super Sky Skater
Minecraft Bukkit Pugin - Let It Rain