I've discovered that it pays to do things right. In the ruby world, this means fixing problems where I find them, making tests and pull-requests. Doing this with languages, I've contributed to ruby and macruby. As far as gems go, I've contributed to cells, rails_admin, rspec and thor. For a more complete idea of my open source work, please see my github account.
MixMatters.com - Programmer and sys-admin February 2011 - Present
A music website for insiders. Has 10s of GB of content uploaded and organised through rails_admin, a gem I've contributed lots to. Custom pages editable with Mercury. Served with nginx, postgres and couchbase. Testing done with rspec and capybara.
Vitae - Designer and programmer. December 2010 - Present
A structured CV publishing system, specifically the one used to generate and possibly serve this CV. Content is defined entirely in YAML. The generator and server are packaged in the one rubygem. Testing done with minitest.
GunnMap - Designer and programmer January 2008 - Present
A web app for making maps of country demographics. Wikimedia has a list of some of the generated maps they're using. Uses rails 4 and D3.js. Previous version made in flex. Testing done with jasmine-rice.
AstroTour - Designer and programmer - December 2007
An interactive, customisable, scriptable, 3D, in browser simulation of the solar system. Written in flex, can load 'tours' defined in a custom xml format.