LevelDB is a fast key-value storage engine written at Google that provides an ordered mapping from string keys to string values. Google has recently announced that they are open sourcing LevelDB under a BSD-style license.

LevelDB is a C++ library that can be used in many contexts. For example, LevelDB may be used by a web browser to store a cache of recently accessed web pages, or by an operating system to store the list of installed packages and package dependencies, or by an application to store user preference settings.

Requirements: -
Demo: http://code.google.com/p/leveldb/
License: BSD License