JustAddMP
adding multiplayer/coop
to single player games
Why we do it
Some of the best games ever made were built for one player. We think they deserve a second.
Featured mod
Mafia: Definitive Edition
Co-op built into the game's own menus. Host from the main menu, invite friends through Steam, and see each other walking, running, armed and driving through Lost Heaven.
- One small DLL, no separate server
- Host and join from the game's own menus
- Invite friends through Steam, or join by IP
- See each other walk, run, draw weapons and drive
- Drop into a host's game mid-session
- 1Run MafiaCoop.exe. It starts the game with co-op built in.
- 2Host from CO-OP → Host Co-op Game in the main menu.
- 3Friends accept your Steam invite, or join by IP.
On the roadmap:NPCsTrafficWeatherMissions
How it works
Single player in, co-op out
Every project here takes a game designed for one and makes room for more.
- 01
Pick a solo classic
We start with great single player games that never shipped with multiplayer, or only ever dreamed about it.
- 02
Hook in & sync
Each mod hooks into the game to sync players over the network first, then more of the world (NPCs, traffic, missions) as the project grows.
- 03
Grab a friend
Install the mod, invite a mate through Steam, and replay the game you love together. Everything lives on GitHub.
Got a game that deserves co-op?
Request a game, open an issue, or send a pull request. Modders, reverse engineers and netcode nerds are all welcome.