You can’t successfully use a home email server.

Mostly true (server can be home but using the ISP network directly probably won’t work)

You can’t successfully use an email server on a (cloud) VPS.

Bullshit

You can’t successfully use an email server on a bare metal machine in your own datacenter.

Bullshit

As such, it is my distinct displeasure to declare the death of SMTP. The protocol is no longer usable. And as we can see, this devolution occurred organically.

Bullshit

Borg for backup. I’m really surprised it’s not more widely known. It’s an incredible piece of software.

Also, not really lesser known software, but a lesser known feature of file systems including the ones we use in FOSS operating systems: extended file attributes - useful to add metadata to files without modifying them.

+1 for Whisper. Also, I use Piper for the reverse (text-to-speech).

Not sure it satisfies your requirements but I’m quite happy with Baïkal.

Borg is great.

Joplin as well, syching my 3 devices with the WebDAV option. I checked a few other options about a year ago and Joplin seemed the best.

A mid-late 24th century Starfleet runabout?

Piper is my choice. Very easy to use from the command line, fairly good sounding voices. Prior to that, for years (decades?) I used espeak-ng, had a very robotic voice but articulated almost everything very clearly, and I got used to it so didn’t actually mind.

I’m very happy with self-hosted Vaultwarden.

Baikal is lean and great. I use it and sync to my Thunderbird (using the TbSync extension) and Android phone (using DAVx⁵).