Here is a very good package somewhat comparable to Adobe Photoshop.. It's free for the LE version, and, not too expensive for the full edition.
http://pixinsight.com/
It's a very extensive program and will take a while to learn how to use all its functions. There are some excellent tutorials available to aid in learning how to do everything you need to know.. It does an outstanding job on images.
For image stacking however, you will still need a seperate program for that purpose. For that I have used Registax, but currently have been using Deep Sky Stacker..
Have A Nice _______