Davens-resolver is a project mainly written in Ruby, it's free.
A simple resolver for resolving from a name to another URL via NAPTR records
This is a simple client that resolves an NAPTR record for a particular subdomain into a URI.
To see the resolver in action you will need to have Ruby installed. Once you have Ruby installed, execute the following command:
bin/resolve twitter.anthony.com
The resolver uses what is known as an NAPTR record, which allows a domain name to be mapped to a regular expression. Resolving a name to a URL is then a matter of looking up a specific name's NAPTR record and executing the regular expression.