Castle aspires to simplify the development of enterprise and web applications. Offering a set of tools (working together or indepedently) and integration with other open source projects, Castle helps you get more done with less code.
Spline.NET is a simple attribute-driven object/relational mapping system built on top of ADO.NET. It is much lighter than typical ORM solutions and allows full access to the ADO.NET APIs, rather than replacing them. It also has a simple IoC mechanism.