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.
About s-expressions, what i read about it: https://web.archive.org/web/20120206034439/https://shinkirou.org/blog/2010/06/s-expressions-the-fat-free-alternative-to-json/
Seems rather niche, for non-key-value-pair data structures (aren’t no-sql databases good for that?), considering that lightweight markup fulfills that role for readable document source.
The appeal for json and yaml is readability, and partially ease of parsing. I say s-expressions win over both in both aspects.
Can you please expand on your references to no-sql and your reference to “lightweight markup”? I don’t quite understand what you meant there.
S-expressions are basically directly writing the AST a compiler would normally generate. They can be extremely flexible. M-expressions were supposed to be programming part of Lisp, and S-expressions the data part. Lisp programmers noticed that code is just another kind of data to be manipulated and then only used S-expressions.
Logo is arguably a Lisp with M-expressions. But whatever niche Logo had is taken by Python now.