CTFs as you need them
One of the best Prodigy hacks
Mangos ZERO is a server for World of Warcraft
PufferPanel is an open source game server management panel
Empowering everyone to host fast and efficient Minecraft servers
Free, Secure, Distributed, Modern Control Panel for Minecraft
Fully async, multithreaded, predictive, open source, 3.01 reach
MCDaemon, a python tool to control your Minecraft server
Minecraft map editor and mod
The Tiny JavaScript Game Engine That Can!
Archipelago Multi-Game Randomizer and Server
Experimental PlayStation Vita emulator
Open source clone of the Age of Empires II engine
A permissions plugin for Minecraft servers
C# application with primary purpose of farming Steam cards
A free/open source client and automation tool for Ragnarok Online
LSJ-Server-Terra (Java Multipurpose Sever connected with MariaDB)
Open source Old School RuneScape client
You can make it - Open Source MMORPG Platform
Magic Another Game Engine
A fancy self-hosted monitoring tool
Python MUD/MUX/MUSH/MU* development system
SRCP system daemon
Classic America's Army