Sometimes it's not an acquittal, appeal, or writ that gets a defendant a favorable result. Sometimes it's a process that goes beyond matters of guilt and innocence. Look below for information on these kinds of processes, where those who've been convicted receive some kind of leniency.
A pardon exempts someone from punishment for a crime. The pardoning power is an inherent right of the people, and they can vest that power in whomever they choose.
Commutation is a form of clemency that reduces the punishment for a crime. It usually takes the form of a reduced ("commuted") prison term, but can also reduce court-ordered fines.