[vaceletm]

For an on prem alternative to Jira, you can have a look at Tuleap.

We (I'm from the dev team) don't aims to re-do a "simple" alternative to jira because there are tons of them and they fall short when things to track get more complex. You can do simple (as github) you can do hellish (as jira) but unlike jira, you don't mandate one model over another (no hundreds of un-necessary fields because someone asked them once).

It's GPL, there is an entreprise plan, it's available on prem and cloud.