[vilaca]

I've seen a few DBs accessible through a REST API.

[berkes]

Several are only accessible through a HTTP REST API, even.

E.g. I'm not aware of an, out of the box, elasticsearch interface that is not the HTTP API.

[danbruc]

This is pure five-minutes-of-serching knowledge, but it seems that Elasticsearch is not a database but a search engine build on top of Lucene.