What Linux "Productivity" (ideally FOSS) tools do you use?

I'm in a bit of a productivity rut and whilst I suspect the issue is mainly between the keyboard and chair I'm also interested in what (FOSS) tools there are that people find effective.

One of my issues at the moment is cross managing different workstreams particularly with personal projects which are more in the "if I have time category".

I'm interested in anything that helps manage time or limit distractions or anything that makes it easier to keep track of progress/next steps for project when there may be a bit of a time gap between.