OPL2 is an open source, extremely moddable replacement for the Polygon Love 2 game engine, written in Python and C++ and using the Panda3D game engine ( www.panda3d.org )
OPL2 is just an engine, you will need the files from the original game to be able to play. OPL2 doesn't contain any copyrighted material from the original game/engine.
While Polygon Love 2 is an erotic/life simulation game, the OPL2 engine does not contain any explicit material itself. OPL2 is heavily moddable and can be used for many other things such as cosplay simulation.
There is a project with the same name but different developers and goals here: http://code.google.com/p/opl2/
Opl2 works good.