A nice article about image processing at Linux, seem all tool are cross platform

http://jane.dallaway.com/articles/GimpPhotography.html
http://www.erikburrows.com/index.php?node=Digital+Photography+with+Linux

After some research, see neat image is the best tools for noise reduction. See if it able to use with GIMP

http://www.neatimage.com/

https://www.google.com/nikcollection/products/hdr-efex-pro/