The Tip of the Day app allows the site administrator to categorize certain content as tips that will be shown to the user on a periodic basis. The app allows the users to turn on/off the display of those tips or launch them anytime from the dockbar.

Overview

The app displays categorized articles.
Allows the user to navigate back and forth between tips.
Allows configuration of multiple categories as tips through Site administration.
Automatically displays the tips on each login or every "x" days, as is established on the Tips of the Day configuration portlet.
Allows tips to be configured on a per site basis

You can see the app´s full documentation here: http://wiki.rivetlogic.com/display/LRA/Tip+of+the+day