Apache Jackrabbit uses Hudson for continuous integration builds. The Jackrabbit builds are a part of the Hudson zone in the Apache infrastructure. See the Hudson wiki page for more information about the Hudson installation at Apache. The wiki page also contains instructions on how to get an account if you're a member of the Jackrabbit Team and want to modify the continuous integration settings.
See the Jackrabbit page on the Hudson server for the list of configured Jackrabbit builds and their current status.
The builds are configured to hourly check the Subversion server for updates and to run builds whenever there are changes. Build and test errors are reported on the dev@ mailing list.