By the creators of Penpot, free plan is basically only missing premium support. Not sure about the login though...there seem to be some plugins for it, not sure how that works with the hosted version?
FYI, Atlassian has a non-profits license. While the cloud version only has a discount so you still have to pay per user, the on-prem version is free. Best part about running on-prem under this license is that a lot of on-prem extensions have opted in to atlassian marketplace licensing and offer free plans for non-profits. While this would be expensive to do in the cloud, because the plugins run on your server, it’s basically free for everyone involved. The downside is you still have to manage and renew licenses, and don’t expect too much support given the free price.
> Atlassian also offers free Data Center (self-managed) licenses for registered charitable non-profit organizations that are non-government, non-academic, non-commercial in nature, non-political, and have no religious affiliation.
More at https://www.atlassian.com/licensing/purchase-licensing#trial... under the faq question about non-profit pricing…
The per-project wiki feature is useful for documentation.
[2] https://docs.tuleap.org/administration-guide/users-managemen...
Edit: in the spirit of the thread, also try Plane.
Unless I'm misunderstanding what you mean by "code level extensibility".
Zammad + Taiga.io|Redmine + Growi|Xwiki + Rocket.chat