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.
Not sure if it counts, but the terminal world being a place where many applications do so many different things but are interoperable, is amazing. I guess that would be the POSIX standard?