Here is a Drupal 6 version of account_reminder. Things look okay so far but please take a look and file an issue if you run into any problems.
A couple of bug fixes, quite important things has been fixed so it's better to make another official release from it.
Differences vs. 6-x-1.1
New features: * Change the behavior of current menu blocks instead cloning all of them!
New features: * Hide Siblings: when you click on a menu item, all other menus close * Much smaller footprint due splitting functions into other files
Bugs fixed: * Single quotes not allowed as menu item's ID
Six dev branch.