We're working on an unofficial multiplayer modification for Mafia: The City of Lost Heaven. Our project is similar to what SAMP/MTA stands for for GTA San Andreas. To bring multiplayer functionality with a lot of freedom for the modders to develop cool gamemodes.
We're finally nearing our first release and I'd be happy to share how the multiplayer looks like so far:
This project involves a lot of reverse engineering in the process as well as figuring out how the sync should ideally work, especially under heavier load. There are several libraries involved. For the server sync, we use our in-house C networking library librg, which uses our custom fork of ENet, that was updated and cleaned up to the modern standards. We also ulilize the CEF library on the client-side, to present the GUI side. Our server backends for serverlist or various services involved make use of the Go language.