twtr.io is an algorithmic URL shortener for Twitter URLs.
Given a full URL to a tweet such as https://twitter.com/aaronpk/status/364781641031360514, this can be shortened to http://twtr.io/bBowYg3hMu. When the short URL is requested, it is algorithmically expanded to a twitter.com URL. Since the shortening is done algorithmically, no database is needed, and the requirements for running this code are very small.
How it Works
The base 10 tweet ID is converted to a NewBase60 number to compress it. The ID is appended to
http://twtr.io/ forming the shortened URL for the tweet.
To un-shorten a link, the NewBase60 number is converted back to its base 10 equivalent. The base 10 ID is appended to
https://twitter.com/_/status/. This takes advantage of a feature of twitter.com where they will redirect a tweet URL to the correct username.
Q: Why do I need this?
A: You probably don't
Q: Where is this used?
A: You can see an example of where this is useful on the IRC logs for the #indieweb IRC channel.