> What are the equivalents for Jira?

Something that gets "close enough", like Mattermost/Rocket.Chat can get to Slack? Probably nothing, given how huge the surface attempt for Jira is.

But for project management and issue tracking in general, there are quite a few alternatives:

  - OpenProject: https://www.openproject.org/ mentioning this first, because it's what I use for my personal needs and feels pretty decent (issue tracking, time tracking, references, comments, files, Wiki, cost reports and so on), though is definitely not nearly as popular
  - Redmine: https://www.redmine.org/ is probably also a really good alternative to mention, while the original UI is dated a while ago there was a project to create something more modern and most of the times when someone is using an alternative to Jira, I've seen it be Redmine in particular
  - Odoo: https://www.odoo.com/ is a more modular system that I haven't really used much personally, but have heard about being talked at the occasional conference in my country, the idea seems nice at least

Also, there are probably a few more lightweight and Trello-like systems for Kanban boards:

  - Nextcloud: also has some apps, like https://apps.nextcloud.com/apps/tasks and https://apps.nextcloud.com/apps/deck that, while basic, can be really easy to get started with if you already have Nextcloud
  - Kanboard: https://kanboard.org/ is perhaps the best Kanban board that I have personally used, just because of how snappy and lightweight it is (at the expense of the features it has, admittedly)

I've also heard of projects like Taiga and Wekan, though can't comment on those due to limited familiarity.

Oh, I also probably should mention GitLab, which has lots of project management features built right into it nowadays, as well as stuff as release management and whatnot: https://about.gitlab.com/features/?stage=plan