Cold fusion. They call it Low Energy Nuclear Reactions (LERN) for short now after that debacle a couple of decades back. There are some technologies that can achieve it at low levels. I know NASA built some rig that could do it to a degree. There are also some theoretical models that report on using lasers to achieve fusion, but I don't know if it's in the experimental stages yet.
RE: What If Nuclear Fusion Breakthroughs Made Nuclear Fusion Obsolete?