Ask HN: Good examples of open source SaaS?

Is Mongo really SaaS? I know Atlas their service for Mongo is but I think of Mongo Community (the Open source project) as a database you need to host. And IIRC the new license prevents anyone from hosting it as a service.

Not trying to be argumentative and would be interested to hear reasons why Mongo Community (the open source part) might be considered SaaS. Maybe my definition is too narrow.