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.