There are a couple I have in mind. Like many techies, I am a huge fan of RSS for content distribution and XMPP for federated communication.
The really niche one I like is S-expressions as a data format and configuration in place of json, yaml, toml, etc.
I am a big fan of Plaintext formats, although I wish markdown had a few more features like tables.
PGP or GPG, however you spell it. You can encrypt stuff, protect your email from prying eyes!
Also FOSS in general.
Huge fan of PHP…I mean PGP, oh god auto correct, you scary 😳