The Aesir project is an open source framework for Massively Multiplayer Online game servers developed using the Microsoft .NET platform in C#, and in essence a rewrite of the current Athena project.
An attempt to fill in the void of affordable/open-source MMO engines written in C#. Newly updated using XNA, Lidgren and a custom physics engine. Checkout the ForgeRealm project which we have now merged with.