OrderEditing.com

We launched this app on Oct 15th, it is now Dec 3rd and 3.5k of our customers have self-serviced their orders in that time. That is a whopping number of customers that didn't need to reach out to our customer service team, and the upsells we've enabled are the icing on the cake.
A genius bit of software, run by some truly inspirations people, who are responsive and attentive. Installing this app is a no-brainer. Truly.