I continue to prefer building a custom queue for anything requiring any features like the ones you describe. I've tried using off-the-shelf queuing systems, and

I continue to prefer building a custom queue for anything requiring any features like the ones you describe. I've tried using off-the-shelf queuing systems, and having the full state of a task being spread across systems (or in other words, having to consult multiple systems to decide if work should be done) produces such a complex, buggy mess. Like anything else, when you need to pierce the abstraction, then it no longer serves you in its current form.