Zulip has long been popular with open source projects (https://zulip.com/for/open-source/), as well as a bunch of other non-business use cases (teaching, research, conferences, etc.). One reason folks might feel like it's new is that we recently reworked the Zulip website to discuss these other use cases for which Zulip is popular.

We have always had a practice of prioritizing feedback and feature requests from open source communities, because improving the productivity of the global open source community is an important part of our mission as an organization.

One of the largest such investments has been the native public access option (no account required!) that we released earlier this month:

https://blog.zulip.com/2022/05/05/public-access-option/

(I lead the Zulip project)