The Castle Project (or Castle for short) is an open source application framework for CLI platform implementations (e.g., .NET Framework).
The project was founded by Hamilton Verissimo de Oliveira (Hammett), who was a member of the Apache Avalon and the Apache Excalibur projects. Keenly interested in the development of an inversion of control container, after he resigned from Avalon and became disillusioned with Excalibur, he went on to develop and release his own for the .NET platform.
Hammett was joined by other developers after publishing a series of articles on Code Project, and the Castle Project eventually expanded its mission "to provide a simple set of tools to speed up the development of common enterprise and web applications while promoting good architecture".
The Castle Project continues to gain acceptance and mind-share from the .NET community, including recognition from Microsoft thought leaders as a framework to assist with building "robust, extensible, working software".