MediaWiki hourlies are snapshots of the ongoing MediaWiki development process and are built from the latest master branch of our git repository. You can download the latest snapshot of MediaWiki from Snapshots. You can also download a so called wmf-version of MediaWiki (something between an alpha and hourly build) which are also used for deployment on the Wikimedia wikis and are built in a weekly cycle. They're available in our git-repository, and can be downloaded e.g. from the GitHub mirror.