Thank you for raising this question. Well, for my things I use MongoDB because of very convenient integration with programming languages (Go, C++ via Mongo C++) and zero hassle with schema

But I'll be happy to replace it by something else, my load is extremely small and only single requirement is to have DB as network daemon, not as embedded storage as it will be used by 2 applications (main daemon an API).

RethinkDB was really nice candidate for it but it's not alive anymore: https://rethinkdb.com/blog/rethinkdb-shutdown/