Difference between Hibernate and NHibernate: Hibernate is the original project. Nhibernate is just a port of the version 2 of Hibernate for the .Net platform.

Hibernate/Nhibernate is an Object/Relational mapping tool which permits you to write much less pure sql, so as to retrieve object graphs for example. In addition, there are some advanced feature like lazy-loading using dynamic proxies (or interception).