The Wiki Rich Content add-on is one of the most widely deployed Alfresco add-ons. It implements valuable functionality that makes the wiki in Share even more useful.
The My Network dashlet visualizes who in your Alfresco network is following whom, and presents that data as an interactive graph of floating balls.
The Share Extras project is the largest umbrella project for add-ons to Alfresco Share. It contains many useful dashlets, customizations, and developer tools. It also serves as a valuable collection of examples for developing your own customizations to Alfresco Share.