eXist-db (or eXist for short) is an open source software project for NoSQL databases built on XML technology.

Unlike most relational database management systems (RDBMS) and NoSQL databases, eXist-db provides XQuery and XSLT as its query and application programming languages.

eXist-db allows software developers to persist XML/JSON/Binary documents without writing extensive middleware.

[2] The companies eXist Solutions GmbH in Germany, and Evolved Binary in the UK, promote and provide support for the software.

[3][4] There is an O'Reilly book for eXist-db which is co-authored by Adam Retter and Erik Siegel.