Android: Using your phone to play music as you drift to sleep is great. Finding out you left the music app running for eight hours is less great. Super Simple Sleep Timer solves this by killing or quieting your apps after a set time.
The app allows you to choose either specific media apps like your music player or Netflix, and set a timer that will force them to close after a set number of minutes. Alternatively, you can select “All” to close everything at once. The timer is fairly spartan, but it does what it does well.