I just noticed that Richard released the last version of Flint. FYI Flint is an open-source project to create a versatile particle system in Actionscript 3. The aim is to create a system that handles the common functionality for all particle systems, has methods for common particle behaviour, and lets developers extend it easily with their own custom behaviours without needing to touch the core code.
Check out bellow examples, which can give you a clear picture of the power of this AS3 PS.
Fire and Smoke