Salix OS

Task Coach
Task Coach is a simple open source todo manager to keep track of personal tasks and todo lists. It is designed for composite tasks, and also offers effort tracking, categories, notes and more.

You'll find the 1.3.24 version, x86_64 package here

Or the SLKBUILD here.

I was pleased to find that Zim Desktop Wiki is still in Salix Xfce, under Accessories. Any opinions about how that compares to Task Coach?

Actually I'm quite unfamiliar with zim. I did not realize it could be used for tasks, I thought it was mainly for notes.

Taskcoach organise tasks (within tasks if you wish) with deadlines, importance, context etc... I was using it with a loose GTD system before I switched to ToodleDo online.