lstu.fr - Another open source link shortener that provides an official instance at the same time
Polr - a quick, modern, and open-source link shortener. It allows you to host your own URL shortener, to brand your URLs, and to gain control over your data.
pygmy - An open-source, feature rich & extensible url-shortener + analytics written in Python.
san.aq - Open-source URL shortener with an HTTP API to shorten long url with curl.