I started using CockroachDB [1] recently and I'm really impressed with it overall. The Postgres compatibility is genius in my opinion, and despite some hurdles it's been a joy to work with (I'm using xo [2] to generate Go code from custom templates). I've yet to deploy it in production, but the best part is that if the performance sucks I can simply deploy postgres instead. As someone who used to be a big RethinkDB supporter, this is my new favorite pet oss project.
edit: oh, and it's written in Go, my main language, which is definitely a plus if you're a gopher