I'm biased (I work part-time for the company), but RavenDB[0] 4.0 is damn fast, cross platform, and has beautiful tooling.

It's built on .NET Core, and our current performance is 140k writes/sec. We also bend over backwards to optimize read speeds: we generated indexes automatically based on your query patterns, discarding unused indexes and throwing server resources behind the hot ones. Also, unlike many other NoSQL databases, we support transactions and atomic writes.

[0]: https://ravendb.net