(MongoDB paid me to write this post. But I was going to write it anyway.)
MongoDB is a highly popular document database (i.e. NoSQL) for powering your applications.
Every app (give or take a few) is powered by a production database
These days, you can choose between something structured (SQL) or unstructured (NoSQL)
Document databases are schemaless – you just throw data in, and worry about it later
MongoDB provides an ecosystem around its document DB – managed services, an IDE, analytics, and search (among other things)