A Joel-on-Software-like forum software written using PHP and MySQL. Open source under a BSD-style licence.

The comments in the post of this page indicate that Amazon.com has a rapidly changing codebase of 100 Million lines of code (LOCs), a large part of which is written in Perl (which is itself considered very high-level and succinct). The maintenance of the code was so demanding that they needed to change from CVS to Perforce because CVS could not scale to that.