They let any open source project with at least 100 stars on GitHub join under their umbrella where they will act as a host organization so that you can start collecting donations (both one-off and recurring) and paying expenses without the headache of setting up a 501(c)(3) and a formal structure. You just add a bunch of trusted admins and you can manage expenses and invoices. Open Collective holds the money for you.
They’re built on open source code themselves and I’ve found then to be very responsive to newbie questions in their open Slack channel.