GameServer is a sophisticated, game server designed for online games
Arianne is an engine to develop multiplayer online games like Stendhal
Source of Mana is a unique 2D MMORPG
online 4X browser game engine
starrydb is game server engine
Game engine allows you to create own MMORPG
LAIR is a Sandbox Dungeon Crawling Game
Develop an emulated Darkfall Online Server.
An Open Engine for use on the OUYA
Open Source Virtual World and MMOG Development Platform
Game Communications Engine
Realmcraft Download (on Engine001.com)
Tikal Online - 3D MMORPG (Torque/Python)
PlaneShift Role Playing Game immersed into a 3D virtual fantasy world