It's called Altwork

https://altwork.com/

That is correct. However, OP says right before:

a great alternative for the kinds of Discord servers centered around Open Source projects and organizations

I find it strange that they themselves have a Discord link in the footer.

Spliit is a free and open-source alternative to Splitwise for sharing expenses. It supports uneven splits, reimbursements, and works as a PWA. Users can use the public instance or self-host their own. Some advanced features are opt-in and rely on external services.

GitHub: https://github.com/spliit-app/spliit

App: https://spliit.app/