Sirix is a versioned tree-based storage system. It provides Snapshot Isolation through MVCC and is best suited for flash-based storage. The tree encoding is suited for heavy update operations. It provides diffing algorithms either to import diffs between currently shredded (imported) XML documents to update a tree structure or to get the differences between versions of a tree structure. A GUI provides several visualizations for comparing imported tree structures.
EJDB is an embedded JSON database engine. It aims to be a fast MongoDB-like NoSQL library that can be embedded into C/C++/Nodejs/Python3/Lua applications. It features collection-level write locking, collection level transactions, string token matching queries, and a Node.js binding.
UnQLite is a in-process software library which implements a self-contained, serverless, zero-configuration, transactional NoSQL database engine.It is a document store database similar to MongoDB, Redis, CouchDB, etc. as well a standard key/value store similar to BerkeleyDB, LevelDB, etc. It reads and writes directly to ordinary disk files. A complete database with multiple collections is contained in a single disk file. The database file format is cross-platform, and you can freely copy a database between 32-bit and 64-bit systems or between big-endian and little-endian architectures.