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This is BETA1 of ACL for Drupal 6.
We do not recommend installing it on a production site, but we encourage you to test it and provide feedback (both good and bad!) in the issues queue. See [#] for details.
Note: The devel_node_access module, which is part of the Devel module, provides an in-depth view into the inner workings of node access, especially if you enable its debug mode at admin/settings/devel#edit-devel-node-access-debug-mode . This is a big help for understanding the forces that are controlling access to any given node.
EDIT: It turns out that I tagged an obsolete version — please ignore this release and use BETA2 instead!