That's a great point and I very much agree on your list, those would be my top choices too indeed.
Other projects that come to mind: #borg, #borgmatic, #autossh - not implying that they're not actively developed, just that they feel like solid components that I tend to set up and then rarely interact with.
A bit more low-level and niche, but same for: #isync, #msmtp, #direnv.
https://www.borgbackup.org/
https://torsion.org/borgmatic/
https://www.harding.motd.ca/autossh/
https://isync.sourceforge.io/
https://marlam.de/msmtp/
https://direnv.net/