Steam emulator for GNU/Linux and Windows that emulates steam online features. Lets you play games that use the steam multiplayer apis on a LAN without steam or an internet connection.
If the latest git build doesn't work you can try one of the old Releases
These Download links have both the Linux and Windows builds in the same package. The Linux builds are built on Steam OS so they should work wherever Steam Linux games work. The latest build is built by the Gitlab CI every time a new commit is pushed to the repo. Right now this is commit: 9b9c440fbc016c9db532b7b57533ff5e68af47e6
There's also a Readme in the zip that you download. Most issues can be easily resolved by reading it (The first few lines are the most important).
IRC channel: #goldberg_emulator@freenode
You can also join it with: Riot
(recommended for people used to the bloated garbage named "discord") or any other matrix client.