My favourite app is a pretty simple little program called "Ringer Volume."
I primarily use it to schedule changes to the volume of the ringer. Monday-Friday I have it set to mute at 9:30 PM and go full volume at 7:00 AM. On weekends it doesn't go full volume until 9:30 AM.
It has a countdown mute timer as well, which is very useful when you want the phone to be muted for a certain period of time. For example, when I go to the movies I set the mute timer to 2.5 hours. That way I don't have to remember to unmute it when the movie is over.