Arianne is an engine to develop multiplayer online games like Stendhal
General Purpose Engine for Graphic Adventures.
Opengate is a Jumpgate remake
plugin-based RPG manager in C++ and Qt5
A 2D Adventure Game & Engine
Star Trek Web browser game
Old School gaming tool for GMs of AD&D/OSRIC.
The SCND Genesis: Legends
Free MMORPG Engine. Develop and host graphical browser-based games.
Table Top Online Role Playing (TTORP)