hamsterdb Embedded Storage is an embedded database engine for C/C++, including wrappers for Java, .NET, and Erlang. It supports in-memory databases, very fast database cursors, "record number" databases, ACID transactions, and duplicate keys. hamsterdb is very fast and highly configurable. It compiles and runs on Unix platforms, Linux, Microsoft Windows, and embedded platforms.
Itzam/Sharp is a C# class library for creating and manipulating keyed-access database files containing variable-length, random access records. Information is referenced by a user-defined key value; indexes may be combined with or separate from data. Itzam/Sharp implements the Itzam engine (see Itzam/Core and Itzam/Java) in 100% managed C#. At 32K, the Itzam/Sharp engine is both small and powerful, and it works with any .NET language, including F# and Visual Basic.
STSdb is an embedded object database system. Its advanced techniques enable organizations to manage terabytes, even petabytes of disparate data within secure, transaction-intensive environments using data management solutions that span a spectrum of challenges: sustaining extreme transaction volumes and tempos and supporting mission-critical analytics and data warehousing.