jsPlumb provides a way to connect elements in a UI.
This page contains examples of the various types of connections you can make.
There are several other demonstrations that offer
a more focused look at some specific part of jsPlumb's functionality - pick one from the drop down or cycle through Next/Previous.
jsPlumb requires one of jQuery, MooTools or YUI3. See the documentation for a more detailed discussion of requirements.
This demonstration uses jsPlumb 1.5.2, MooTools 1.3.2 and MooTools More 1.3.2.1