A lightweight online game framework
Arianne is an engine to develop multiplayer online games like Stendhal
GameServer is a sophisticated, game server designed for online games
A server software reimplementation for a certain anime game
LGSL (Live Game for PHP 5.4-8+: online status for various gameservers
Massive Multiplayer Online Wargame Leveraging the Internet
Massively multiplayer online game server and client framework
Create your own online real-time browser-based MMO in your website