MongoDB is an open source, high-performance, schema-free, document oriented database.
It has been written in C++ as a document-oriented database, so it manages collections of JSON-like documents.
MongoDB supports cross-platform support (Windows, Linux, Solaris). It also has a rich set of data types (supports dates, regular expressions, code, and binary data).
MongoDB uses memory mapped files. For Windows the data size is limited to 2GB on 32-bit machines (64-bit systems have a much larger data size).