It's exactly like water. Use their API, and you pay as much water as you drink. But visit them in their pub, and you get a pretty big buffet with lots of water for a one-time price.

There is also Procrastinate: https://procrastinate.readthedocs.io/en/stable/index.html

Procrastinate also uses PostgreSQL's LISTEN/NOTIFY (but can optionally be turned off and use polling). It also supports many features (and more are planned), like sync and async jobs (it uses asyncio under the hood), periodic tasks, retries, task locks, priorities, job cancellation/aborting, Django integration (optional).

DISCLAIMER: I am a co-maintainer of Procrastinate.

I’m using Procrastinate in several projects. Would definitely like to see a comparison.

What I personally love about Procrastinate is async, locks, delayed and scheduled jobs, queue specific workers (allowing to factor the backend in various ways). All this with a simple codebase and schema.

it should be the opposite of procastination, but good naming anyway.