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.
They’re “file like” in the sense that they’re exposed as an fd, but they’re not exposed via the filesystem at all (Unlike e.g. unix sockets), and the existing API is just mapped over the sockets one (i.e. write() instead of send(), read() instead of recv()). There’s also a difference in how you create them, you open() a file, but connect() a socket, etc.
(As an aside, it turns out Bash has its own virtual file-based wrapper around sockets, so you can do things like cat a remote port with Bash, something you can do natively in Plan 9)
Really it just shows that “everything is a file” didn’t stand up in practice, there’s more stuff that needs special treatment than doesn’t (e.g. Interacting with TTYs also has special APIs). It makes more sense to have a better dedicated API than a generic catch-all one.
