The Helios Project is a Ragnarok Online emulator. Unlike most emulators, this one is from scratch, uses multi/single server exes, the Lua scripting engine, and many more features.
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.
AdAge4 is a content module for the gCraft MMO Engine. gCraft can also be found within this project. gCraft will be a generic engine programmable in Lua/XML to provide an easy to modify gaming environment.
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.
Eternal Warfare is turn driven, browser based game. It will have multiple realms to play through and eventually travel back to. Development will be focused mainly on community driven systems and will also create a flexible character development system.