SockTalk is a socket-based, SSL-enabled IM library that can be used to create IM programs. A command line server program and a client program are included in the C++ and Swift repositories. One machine runs the server program and other users connect via the client program. Each user can specify a username and the chat can be hosted on any open port. Commands are used to disconnect, display connected users, etc. More details are available in the README. The QML frontend repository only contains a client frontend.
SockTalk is written in C++ and should be compatible with any desktop platform. The program has been run on Ubuntu 16.04 LTS and Mac. If it turns out it uses a platform specific library or feature, please let me know by opening an issue.
Tested platforms:
The Swift version of SockTalk is designed to be used on Mac. The Cocoa frontend is Mac-only, but the backend could become compatible with any platform depending on the progress of projects to make the Foundation library open source. The Swift version has not been tested on any other platforms.