... API endpoints with curl and use rsync to store backups of your contact list on a remote server. Install what you want through the APT package management system known from Debian and Ubuntu GNU/Linux. Why not start with installing Git and syncing your dotfiles? Have you ever sat on a bus and wondered exactly which arguments tar accepts? Packages available in Termux are the same as those on Mac and Linux, install man pages on your phone and read them in one session.