NetGore is a free, open-source 2D online RPG engine written in C#. It is cross-platform and supports both top-down and sidescroller games. NetGore comes with a large amount of the fundamental MMORPG components built in which allows you to focus more on designing your game.
(view more images)
Purpose: The idea behind NetGore is to provide a strong foundation to build a game off of, and to provide the implementation of all the fundamental components involved in 2D online games. That way, people can spend their time with what makes their game unique and stand apart from the rest. For the past few years, the focus has been on performance, flexibility, and advanced features. Recently, the focus has shifted to making it even easier and faster to create your own game with NetGore.
Target audience: NetGore is intended for online multiplayer 2D games only. Although the focus is mainly on real-time RPGs, most any kind of multiplayer 2D game is fine. Some users have already implemented shooters and turn-based combat. We also focus especially on indie developers in numerous ways, such as by including a lot of the features for you and providing a fully-functional base game to work off of.
Features: A detailed list of features can be found on the about page, but in short, most of the basic (and some more advanced) MMORPG features are built in to the engine. More features are always being added as well based on the demand for them.
Any feedback is appreciated, either here or through the NetGore forums.