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.
I have never understood why you can delegate a subdomain but not the root domain, I doubt it was a technical issue because they added support for it recently via
SVCB
records (But maybe technical concerns were actually fixed in the decades since)