Self-hosted game stream host for Moonlight
Arianne is an engine to develop multiplayer online games like Stendhal
A server software reimplementation for a certain anime game
A fast, scalable, distributed game server engine/framework for C++
Free MMORPG
Massively multiplayer online game server and client framework
Nexuiz-Xonotic Client
Proxy for games that emulates network conditions like ping and lag.
Create your own online real-time browser-based MMO in your website