Subversion read access
Allegro's source code is maintained in a Subversion repository. You can get clients for most platforms at http://subversion.tigris.org/, and there is good documentation like the Version control with Subversion manual.
The main URL is:
https://alleg.svn.sourceforge.net/svnroot/alleg/
Use one of the following commands to check out a stable branch:
svn co https://alleg.svn.sourceforge.net/svnroot/alleg/allegro/branches/5.0
svn co https://alleg.svn.sourceforge.net/svnroot/alleg/allegro/branches/4.4
svn co https://alleg.svn.sourceforge.net/svnroot/alleg/allegro/branches/4.2
Use one of the following commands to check out an unstable branch:
svn co https://alleg.svn.sourceforge.net/svnroot/alleg/allegro/branches/5.1
SVN::Web Interface
You can browse the source code online at http://svn.tomasu.org/index.cgi/allegro. It uses a mirror so may only show commits up to 5 minutes later but the site may work faster than the ViewVC access at Sourceforge.
ViewVC Interface
You can also use a web interface to browse the repository directly at http://alleg.svn.sourceforge.net/viewvc/alleg/.
Test results
Daily SVN test results can be seen here: http://allefant.com/tests.py
Upstream tracker
Shallow test results from the Upstream Tracker: http://linuxtesting.org/upstream-tracker/versions/allegro.html
Changelogs of the Subversion tree
The SVN repository also has a commit hook for CIA, a system for tracking open-source projects in real-time. The CIA web interface provides an RSS feed and notifications in the #commits channel on the Freenode IRC network. You can monitor Allegro activity at http://cia.vc/stats/project/alleg.