[mrweasel]

It's really hard to find any product or suite of products that replaces Atlassians offerings. Sure you can easily find a issue tracker product, but can it be a service desk at the same time? Bitbucket, Confluence and Jira also integrates really really well. You can have entire workflows that just makes sense, link to documentation, pull-requests/commits and tickets. I've frequently used this setup in a ITIL environment, entire workflows where you have tickets for test, staging and production deployments, the production deployment is a ticket that have the relevant pull-requests linked and the documentation is automatically updated because everything works together.

There's a number of companies offering "Jira replacements" at it's either just service desk features or a ticketing system, almost as if the authors never really used a full-blown Jira (/Atlassian) setup.

People complain a lot about the UI and speed of Atlassians products, but on-prem isn't really slow, even with a ton of plugins, but you do need trained staff to manage it. The UI is because of Jira doesn't really impose much in the way of restrictions on how to use it. You can basically mix and match anyway you like, service desk tickets mixed in with SCRUM workflows... doesn't mean you should, but you can.

[nvm0n2]

You can configure JetBrains TeamCity to be a service desk and competent issue tracker, it also has a Confluence-style knowledge base in the latest versions.