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 and many others use it! And Google, meta, etc. Have used it but decided to lock it down.
Yes you’re right, there’s a reason people don’t use it as much, which is because these corporations embraced it, dominated it, then extinguished it.
But XMPP is honestly my favorite comm protocol and the most impressive imo.