2Moons, a PHP/MySQL engine, a heavily modified engine based on XNova with a design & game mechanics inspired by OGame.
Quite a nice engine inspired by OGame, quite well written (OOP PHP, jQuery, and so on), only it lacks some more outstanding features of other similar engines, for example factions (races).
Generally, more of a rip-off of OGame, but it fills some gaps by adding some new technologies and units. ;-)