Each version of Pressflow is API-compatible with the same major Drupal version. For example, Pressflow 6 is compatible with all Drupal 6 modules. Pressflow 6 also integrates the SimpleTest system from Drupal 7 and the CDN support patch.
Early work for Pressflow 7. Do not use for external projects because this uses Drupal.org's git repository, which lacks stable hashes.
This branch is obsolete. Pressflow 6 now tracks the official Drupal git repository.