Trello: Project Management Tool
I've used a handful of tools in order to keep track of projects and things I should be working on, but so far Trello has been my favorite. Its interface is simple and modern.
In it, you are given a board on which you put categories, then in those categories you put cards (or tasks). You can move your cards around as you progress on your projects and give them color-coded labels. It doesn't just have to be for personal tasks and can be collaborative for group projects. Integrations such as Google Drive are available.
It's easier to understand Trello through visuals than text, so here is a screenshot from an example involving a team creating an app for dogs.
You can view the rest of this board and check out Trello here: https://trello.com/b/R6DSCtsw/building-an-mvp-barker