Ask HN: Powerful open source frameworks for Hack language?

I spent around a year programming in Hack for a large customer of my company. There is a lot I love about this language. I would love to build some cool things in it on my own, but I'm having trouble figuring out just how much of my own stack I would have to roll in order to do it. This is made all the more difficult by the language's name being really tough to Google.

Are there any standout frameworks out there for building awesome things in Hack?