the shortest thing that could possibly work

Mike Migurski has coded up the simplest possible self hosted URL shortener, and published it on github

One of the small tools that I think would make rev=canonical even more useful is a rapid, brainless way to create short URLs for any domain. It’s possible, in a brief PHP script that only knows how to speak HTTP, to:

1. Redirect from short URLs to long URLs
2. Respond with a short URL for a given long URL
3. Add a new short URL for a given long URL