I'm no expert in this, but from what I've seen, most of the small players are working on variants of aneutronic fusion[1] a method that reduces the quantity and energy of the neutrons that come out of the reaction. There you have Polywell Fusion, Tri-Alpha Energy, and Lawrenceville Plasma Physics (Who are supposed to be running tests on their device this month).

There's also Helion Energy[2], which is a YC startup, but their process seems to involve some sort of magnetic reflectivity from the fusion reaction.

[1]http://en.wikipedia.org/wiki/Aneutronic_fusion [2]http://www.helionenergy.com/