MonoRail (formerly called Castle on Rails), a component of the Castle Project, is an open source web application framework built on top of the ASP.NET platform. Inspired by Ruby on Rails Action Pack, MonoRail differs from standard ASP.NET Web Forms development by enforcing separation of concerns using a model–view–controller (MVC) architecture. The framework is commonly used in conjunction with Castle ActiveRecord, an ORM layer built on NHibernate. In January 2010, version 2.0 of MonoRail was released, however, many projects use the trunk version of the source to take advantage of new features without waiting for official releases.