Twisted's continuous integration solution is BuildBot. BuildBot runs the Twisted test suite (as well as a couple other tasks) each time a checkin is made to Twisted trunk (and can be asked to do the same for a branch checkin). This provides developers with immediate feedback about their change across a wide array of platforms and Python versions. If a test suite failure is ever reported on any supported platform by BuildBot, the checkin which introduced it is backed out until the failure can be fixed.
A build slave is a long-running program that connects to the build master and executes jobs the master sends to it. A build slave needs to be online almost all of the time. An offline slave creates uncertainty about whether Twisted trunk is in working order or not.
If you have a host with good availability, operating a slave is an easy and helpful way to contribute to Twisted.
The slaves connecting to Twisted's BuildBot master run in a variety of platforms. These platforms determine what the supported configurations of Twisted are.
As well as running the Twisted test suite, BuildBot also runs coverage reporting tools to generate reports of how much of Twisted is covered by its test suite. The configuration for these slaves is similar to that of normal test slaves, but there are a couple extra dependencies.
BuildBot also generates Twisted's API and howto-style documentation. These development snapshots are available for people looking for the most bleeding edge Twisted documentation.