A URL shortener is not that hard to write. At the most basic level it's one table with key = the url blob and value = the url target. There's already several hits for 'open source url shortener' in the top results there's one with MIT and one with GPLv2, and several others that don't specify their license.

This one is neat because the author chose to restrict to the qr code "alphanumeric" character set that includes a couple symbols to reduce bits per character in the encoding. Now that you're aware of that, you could certainly do that yourself or modify another shortener to do it.