SMM++ Mud Client is a mud client with extended and unique features. Aside from all standard mud client functionality like ANSI color support, aliases, action triggers, and tab-completion, SMM++ features a highly-customizable user interface (labels, buttons, and menus) and unique and powerful mapping capabilities, and SMM++ is the only mapping crossplatform (Tcl/Tk based) mud client available.
EQEMu EverQuest Server Emulation Project is a project designed to fully emulate the EverQuest servers for use with the EverQuest(tm) client. This allows users to use their EverQuest(tm) client to connect to "unofficial" servers or to run their own EverQuest(tm) server. It is currently being developed for multiple platforms.
OpenMW is an attempt to reimplement the popular role playing game Morrowind. It aims to be a fully playable implementation of the game that will run on Linux, Windows, and Mac OS X. No game data is distributed with the code; the user must already own a copy of Morrowind to use the software.
Arx Libertatis is a cross-platform, open source port of Arx Fatalis, a 2002 first-person role-playing game developed by Arkane Studios. Arx Fatalis features crafting, melee and ranged combat, and a unique casting system where the player draws runes in real time to effect the desired spell. The Arx Libertatis source code is based on the publicly released Arx Fatalis sources. This does however not include the game data, so you need to obtain a copy of the original Arx Fatalis or its demo.