GalGen Trader is (or at least will be) a 2D space trading and exploration game set in a complex and persistent procedurally-generated universe. Dwarf Fortress in space, if you will.
One of its most important features is the ability for extension modules to be added that can change just about any feature of the program; from new weapons and devices, to adventure modules that add new 'mini-plots' (similar to the Galactic Adventures DLC for Spore), to modules that replace parts of the core game...