Short bio: Computer Scientist, FOSS supporter (read more)
Tux Machines (TM)-specific
One excellent open-source program that often gets overlooked in the focus on products like Linux is The Gimp. GIMP is an acronym for GNU Image Manipulation Program. It is freely distributed software for photo retouching, image composition and image authoring.
I have been using the open-source Thunderbird for my e-mail but I had not used the Gimp until a friend of mine and old Database columnist pointed me in the right direction.
The place to start is www.gimp.org, where you can get the Windows, Mac or Linux version and the documentation.