Fusion
Hint: OSE's stand on fusion energy: There is no such thing as radioactivity-free fusion. Even so-called a-neutronic reactions have neutrons associated with them, if not direclty, but by side reactions. Energetic neutrons have the property of breaking apart other neutrons. So there is no known way to harness fusion energy safely, unless we discover new laws of physics. So unless we accept nuclear radiation hazard as part of life, fusion is out of the question - just like fission. I don't think a case can be made that fusion or fission is appropriate technology, given that we have solar energy and hydrogen. -MJ
Overview
Fusion is the process of combining nuclei, thus creating energy. Sustained fusion has been achieved many times by many different groups and people, but a fully functioning reactor that generates more power than is consumed has yet to be produced.
Open Source Community
Simple fusors that create the radiation which power can be extracted from have existed for year, and there exists a growing community dedicated to making them. Most of these focus on creating a Farnsworth–Hirsch fusor. Recently, several people have started making home-made polywells, taking advantage of new 3D printing techniques.
Coulter's Smithing is a project focusing on open sourcing a nuclear fusion reactor.
