 <p>No, I don't know of any. Because NHibernate is popular and very good at what it does, and EF is likely to pick up most of the remainder (particularly devs that don't want to stray from Microsoft-supplied frameworks), the barrier to entry for a new player is very high. Another ORM would need to add something significant over and above what NHibernate currently offers in order to get any reasonable level of interest. </p> <p>If there was an open source project that wanted to deliver better Linq support in an ORM, in my opinion it would have greater success contributing to NHibernate Linq rather than attempting to build its own framework from scratch.</p>