Millions worldwide play the popular, commercial, open world game, Minecraft. Players build constructions out of textured cubes in a 3D, procedurally generated world. Minecraft is being used in many schools today and for various subjects, particularly the humanities. But cost and a lack of training have been barriers for schools looking to use a proprietary game like Minecraft in the classroom. Open games, or games offered freely by non-profit organizations, by contrast, do not often have these same barriers. Moreover, the communities involved with these open games is a golden educational opportunity for teachers to use with their students as a lesson in participation and sharing. SourceForge is a resource for numerous open source MMO games to download for free.