ThoughtWorks' consultants will be working on a bunch of open source projects after work. Come and work with them on their projects, or bring your own.
ThoughtWorks was the first sizable consultancy to switch to Agile (mostly XP) methodologies in 2000, and even for open source they prefer test driven development (TDD) and related practices.
The emphasis will be on actual commits.
Leading the evening for ThoughtWorks is Paul Hammant who is ThoughtWorks chief open source zealot. He's also co-counder of the original London Geeknight, co-founder of PicoContainer (a Java Dependency Injection container), and co-founder of Selenium, which is the defacto-standard open-source web testing technology and multi-language.
ThoughtWorks is going to lay on food. Most weeks that's going to mean Pizza.