Dovel is a simple and extensible SMTP server that let's you send and receive email using a self hosted instance with minimum configuration. Dovel is free and open source software written in Go.

Manage and view runit services. Specifically made for voidlinux.

An exhaustive introduction book for the fossil version control system.
Goes over not just the cli how but also a lot of the 'why' which is one reason I really like it (and some of its points really apply to more than just the fossil scm).