Awesome app! Absolutely love it!
Very useful if you have things to do. It also kind of serves the purpose of a planner.

I've been using ToDoist for about a year. It's great, meaning I can do everything I can possibly think of with this app regarding managing my tasks. Plus it's easily accessible via Chrome or Firefox and I can easily turn Gmail emails into to-do's. The only relatively minor issue: I don't use the Windows 10 App (I use it only in the browser) because there apparently is no way to adjust the font or screen size within the app; the default is too big for me.

This easy to use Task Manager works across platforms, so it automatically syncs my Firefox, my Android, my Windows at work, and other places. It sorts and filters by "Projects" (I like to say contexts = where I need to do the task) and tags (which can be assigned ad libitum).
Altogether, after trying several online task managers, my favorite.