If you're a freelancer or a small dev team and are feeling unorganized, I'd recommend to use Streber PM (project management). I've been using Streber for the last year or so, and I find it completely adequate. Very simple to use and a clean design (which is important IMO).
Users can create projects, tasks, topics, milestones and much more. It's great to use for any size of projects, and has tons of options.