The last year I have ben using the Siril software to pre processing my astrophotos. It replace somewhat AstroImageJ and Fitswork I used a lot earlier. Siril is based on Iris which I used 20 years ago, very advanced at that time. Siril is today a 32-bit processing software and in these days an updated version 1.2.0 beta 2 is out. My tutorial isn't very deep and I'm still learning. There are already a good homepage with examples how to use Siril, my page is more how I personally use it.
http://www.astrofriend.eu/astronomy/...ial-siril.html
What I like is the color calibration and the new function to desaturate overexposed stars. Much to learn until it work perfect.
For post processing I use the Gimp software which also is a 32-bit software and very advanced.
Both Siril and Gimp are free to download.
/Lars