I use my calendar for scheduling important events. I use the play music app for concentrating on tasks such as tidying and cleaning dishes.
I don’t use an app anymore, but a Happy Planner and I find myself getting more things done with a to do list made with pen and paper than I did before using an app.
I've used todoist for a while, but now I've switched over to a journal. I still use the inbox in todoist to capture thoughts and things I need to do whenever I come up with them. Every morning I go through the inbox and write what I need to do that day in my journal.