Ender Lib creates an abstraction that emulates threads in Flex and Flash. While not physically possible to do in the Flash Player, much to our dismay, we can still roughly approximate them with a framework that provides yielding and scheduling.
In many cases, such as socket processing, events replaces the need for threads in AS3. However, in cases where long-term processing needs to take place, Ender Lib can emulate threading that will avoid apps that appear to "freeze".
There are just a small dash of rules for how to write your threaded routines, but if you follow it then all the special code needed to approximate threading will be done for you in a flexible framework!