suc is a Simple Unix Chat system that offers core features similar to Slack, Mattermost, and IRC. It achieves this with just five lines of bash code. The simplicity of suc is in contrast to the massive line counts of other chat systems like Mattermost, which has over half a million lines of code. Suc leverages SSH, UNIX’s access control API, and UNIX’s text-based modularity for features like authentication, access control, and encryption. It utilizes ANSI escape codes for displaying rich text and can be extended using usuc, a separate binary with more features. Overall, suc demonstrates that less code can still provide powerful functionality.
https://the-dam.org/docs/explanations/suc.html