This module wants to end the situation of current D6, where hook_init() is a crowded battle place. Things like drupal_add_js(), drupal_add_css(), etc, can now be done in hook_pageapi(), instead of hook_init().
One major goal is to prevent premature theme initialization, premature menu_get_item(), and other things that we don't want to happen too early in a request.
Status / stability
The API of this module is still taking shape. See the discussion on groups.drupal.org
First release(s) of this module will be stable enough for use with DQX AdminMenu, which is going to have pageapi as a dependency.
Those aspects of the API that are not used in DQX AdminMenu are carved in chewing gum. Especially, method names and signature of the $api object. You only need to worry about this, if you use/develop other modules that use pageapi. In this case, you are welcome to join the discussion on groups.drupal.org.
How it works