Python game template
Card, board & tiles making Software
Map and logic editor
Andruill Engine is a GMS (Game Management System) written in PHP.
An extensible game engine that targets RPGs.
CM Game Development Kit
Isometric engine for 2D rendering with XNA and SDL
A 2D Java game engine
A small Game Engine project.
The next generation mud is an open-source extensible, programmable mud
The Objective-C Interactive Simulation Abstraction Layer
A generic C++ MUD server featuring a strategy-style hexagon map