The Eisenhower Matrix—so named because it was used by Dwight Eisenhower—is a technique of visualizing and prioritizing decisions by marking them urgent/non-urgent and important/non-important. If you mark each task with the two attributes, it will fall into one of four quadrants: important/urgent, important/non-urgent, non-important/urgent, non-important/non-urgent. The quadrant a task falls in helps you decide when, if ever, to deal with it. Take a look at the link above to see the details.
A few years ago, Tom Purl wrote a short post showing how to implement the Eisenhower Matrix in Org-mode. His system works pretty much the way you think it would. He has two potential tags for each task: “important” and “urgent”. The tasks get tagged with 0, 1, or 2 of the tags, which effectively puts them in one of the quadrants.
The rest of the system is a set of four agenda searches, which he labels “1”, “2”, “3”, and “4”. For example, the “2” search looks for the tags “+important-urgent”. Take a look at Purl’s post for the others if you are in any doubt.
The idea is simple but effective. If you’re looking for a way to get a handle on your tasks, first read the Eisenhower Matrix article and then Purl’s post for a simple implementation. You won’t need any fancy websites or apps: just Emacs.