From Drupal and Moodle, right through to a Git versioning system and Perl modules on CPAN, we contribute back to over 175 community open source projects. This list is in order of the number of projects contributed to.
Faster, easier client and server-side form validation for SilverStripe
simple chaining hash table implementation written in pure C (c99)
Kernel for I9300
A collection of snippets for snipmate
Console interface to Gerrit Code Review
A php swagger annotation and parsing library
Test::BDD::Cucumber - Cucumber in Perl
the /tg/station branch of SS13, a byond based 2d game about how to keep a station full of insane people alive for more than 20 minutes.