Volante is a free, small, fast, object-oriented, NoSQL, embeddable database for .NET.
See http://blog.kowalczyk.info/software/volante/ for more information.
Volante is a continuation of Perst database. Perst was licensed under liberal BSD license until version 2.49. In version 2.50 the license was changed to dual GPL/commercial license.
Volante is a fork of the latest BSD-licensed version (2.49) and is now developed independently of Perst, preserving liberal license, so that you can use it in both open-source and commercial code for free.