Our CI system is powered by Jenkins. For Apple’s platforms it builds and runs tests for OS X and the iOS simulator. For Linux it builds and runs tests for Ubuntu 14.04 and Ubuntu 15.10 (both for x86_64). In addition to using it for testing active branches, the CI system also produces the snapshots that are available for download from Swift.org.
CI is not only a powerful tool for monitoring the health of the Swift project, but can also be used as a part of reviewing changes before they land. To facilitate this, we have integrated testing within pull requests, allowing testing to occur before commits are made and without destabilizing the
masterbranch. The results will be posted inline within the pull request. When someone makes a change that breaks a build, they will automatically be notified via email.
More details at the Swift.org blog.