We also use Postgres but we don't have many jobs. It's usually 10-20 squedule that creates hourly-monthly jobs and they are mostly independent. Currently a custom made solution but we are going to update it to use skip locked and use Notify/Listen + interval to handle jobs. There is a really good video about it on YouTube called: "Queues in PostgreSQL Citus Con."

pikku means tiny or little in Finnish. Is it where the name came from?

I don't know but my first association was "pico-dokku"

My guess has been they both originate from heroku; docker heroku to dokku, pico heroku to piku

Cute, as in the sibling language, Estonian it means “big” or “tall”

Nope. https://piku.github.io/FAQ.html