Is there any way to migrate away from Jira, or is it full lock-in? I mean, is there any migration tool or service to Redmine, Gitlab, MantisBT, Trac or whatever

Is there any way to migrate away from Jira, or is it full lock-in? I mean, is there any migration tool or service to Redmine, Gitlab, MantisBT, Trac or whatever? I think one reason Atlassian was successful is that they always invested a lot of effort in building tools to migrate to their products from any of their competitors (obviously not the other way around).