What does this extension?
This extension adds a new select field in the access tab of the pages and tt_content tca, which allows you to select usergroups. The element will be hidden, if a logged in user is assigned to one of the groups.
You can set a TCA column as "fe_group_inverted" within the "enablecolumns" ctrl section. This will do the same features as described in point 1.
There is a new TypoScriptFrontendController function named: checkPageGroupAccessWithParents