Mongo, whose name comes from "humongous”, is a database aimed at developers with fairly large data sets, but who want something that’s low maintenance and easy to work with. It’s a document-oriented system, with records that look similar to JSON objects with the ability to store and query on nested attributes. From my own experience, a big advantage is the proactive support from the developers employed by 10gen, the commercial company that originated and supports the open source project. I’ve always had quick and helpful responses both on the IRC channel (irc://irc.freenode.net/#mongodb) and mailing list, something that’s crucial when you’re dealing with comparatively young technologies like these.
It supports automatic sharding and MapReduce operations. Queries are written in JavaScript, with an interactive shell available, and bindings for all of the other popular languages.
Quickstart MongoDB documentation
