MongoDB

 MongoDB  is server-side database software used for storage in some CMSes.

IndieWeb Examples
IndieWeb community members using MongoDB for storage with their projects:

Ben Werdmuller
's werd.io runs Known with MongoDB since 2013-05 (werd.io launch, just before IndieWebCamp 2013).

Michael Owens
uses Indie.js on mowens.com which has used MongoDB for its data store since July 2014.

Past IndieWeb Examples

 * none yet (possibly at some point when he switches werd.io from MongoDB to MySQL)