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.
It’s the recommended approach to replace WCF which was deprecated after .NET framework 4.8. My company is just now getting around to ripping out all their WCF stuff and putting in gRPC. REST interfaces were always a non-starter because of how “heavyweight” they were for our use case (data collection from industrial devices which are themselves data collectors).