Thankfully, there's a free tool that can help. I started using Asana around a month ago, and it has already made a world of difference for me. And, yes, it has a great app too.
In terms of my own work, I can schedule out tasks with dates by which they should be completed or leave it open. Either way I have a handy list of everything that needs doing and even reminders when something is coming up. Have a big product launch or a specific push happening? You can create a project and even add collaborators directly do it. Speaking of collaboration...
In my freelance work with Dusk Comics, I help manage a team of student interns. It can be hard simply remembering who is doing what for whom and when. This way? We all stay on the same page and can even view a calendar of the items that need to be done. Again, the ability to make a special project for big pushes like the "Bump Day" you see on the sidebar make it really easy to make sure all aspects of a particular job are being covered.
Whether you've got a whole team to manage or just yourself, I highly recommend checking Asana out. It's free, it's pretty intuitive, and it can help you get that mountain of "to do" memos under control.