[ Thanks to Dart for this link. ]
“Vapor is a cross platform steam chat client written in C# which
allows you to chat with your friends on Steam. It does not have any
other feature but is useful if you want to stay in touch with your
friends while using Linux distributions.“Vapor Client is developed by VoiDeD using a free and opensource
project SteamRE that implements networking using SteamKit2 library.
Both Vapor and SteamRE are work in progress and new features will
be added in future.”