I’ll cut right to the chase, Copyq, syncthing, and tldr.
Copyq, at https://hluk.github.io/CopyQ/, is a clipboard manager for Linux, Windows, MacOS, AND ChromeOS in the Linux environment! It has a GUI as well as a command-line interface and in the ChromeOS environment, captures clips from BOTH Linux and ChomeOS! CHeck out the docs.
Tldr, at https://github.com/tldr-pages/tldr, provides a cheat-sheet-like summary of command options. It’s not as full function as a man page but can often provide just that one bit of info you need. It provides info on Android, Linux, MacOS, Windows, Sun OS(!), and a set of common commands like 2to3 (convert python 2 code to python 3), adb (Android Debug Bridge which can be installed on many different platforms), and atom (a cross-platform editor).
Syncthing, at https://syncthing.net/, is an open source, multi-platform, authenticated, continuous file synchronization program with communications secured by TLS. It works on MacOS, Windows, Linux, Android among many others.