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.
And also, the Dekatrian calendar
Where we would have a less broken, more regular, year calendar that is almost align with the moon cycle.
Oh many years ago in school I created something like that for an arts/creative writing project once, a calendar with 12, 30 day month based on sailor moon. Having it based on a magical girl manga gave me the freedom to declare the rest of the days to “days of evil” Was a fun project because I created a whole religion around it. 😁