As far as I know HashGraph is a privately owned technology. I think I read somewhere an open source version may be in the works.
Iota also is working on a similar technology. It is called the Tangle. Might want to give them a look.
I've seen this one. This ICO might become great project this year. A lot of ICO rating and ICO analysis talk about this ICO. I saw that they give a good rating for this ICO. Honestly, I still not much-digging information about hasgraph. Maybe later I'll do it my own research.