Subversion
Subversion is a version control system. Basically, a fancy folder on the internet developers use to manage their projects.
To grab a copy of the bleeding-edge version of Allegro#, you'll need a Subversion client. If you're unfamiliar with Subversion, TortoiseSVN is the way to go.
The main repository can be found at:
http://svn.lessthanthree.vg/AllegroSharp
But chances are you'll just want the trunk, which is found at: