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.
Linux kernel for Texas Instruments OMAP series of processors
Linux source for Allwinner/Boxchip F20 (sun3i), A10 (sun4i) and A12/A13 (sun5i) SoCs.
The official Linux kernel from Xilinx
melo's cil (http://kapiti.geek.nz/software/cil.html)
DVCS-powered ticketing system
Moodle 2.x My Courses block - an alternative to the Course Overview block used on "My" Homepages.