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.
libosl, the object storage layer, is a library for storing small to medium-sized data in relational tables. It is easy to use, lightweight, fast, and portable. libosl is suitable for applications that need only a small fraction of the features a full database management system provides.
SMDB is a small, portable database library that exports an API similar that of GDBM and allows for the simple storage and retrieval of key/data couples. The library is totally system independent due to the use of externally supplied interface pointers. File locking is left to the caller, allowing single instance users to not pay the the price (in terms of performance and portability) of the locking framework. It supports transactions, multiple tables inside the same DB file, and is less than half the size of GDBM.
lib4d_sql is a C library that provides the required functions (connect, prepare, execute, etc.) for writing an SQL client for 4D databases. It uses the public 4D SQL protocol, which is supported by 4D products since version 11. It is already used by the PDO_4D Open Source project, and it might be used to provide others drivers for JDBC, ADO, or ActiveRecord.