[zeroDivisible]

Well, I think I must disagree with you in here.

I'm sure that it is a viable choice for some use cases, it's just that I didn't found a use case for it yet.

Being able to choose from PostgreSQL, Redis, Cassandra, heck, even ElasticSearch made me always choose one of those over MongoDB, at least for the problems which I had been trying to solve.

[mutex007]

By the way if you are looking for all the above functionality provided by all the DBMS you mentioned in a single DBMS instance, you can check out amisaserver.com. Polygot persistence is just another fad.

[wilsonfiifi]

Doesn't appear to have a community edition for local/private installation...

[orthecreedence]

Don't forget RethinkDB. Very good general-purpose document store that supports joins and has an excellent query language (no DB write lock either!)