Operating Systems from Microsoft and Apple both have Adobe products available. More specifically Lightroom and Photoshop. Both programs are more that sufficient at post-processing, if not the professional standard. Photoshop is geared toward the heavy editing aspect of pictures, and Lightroom is geared toward organizing and lightly processing images. For Mac, you can use their own software called Aperture, which is probably most like Adobe Lightroom with the level of editing features available. I have never used either of those two programs. Because I have always been happy with Photoshop, I can’t really give you any solid suggestions as to which program is best for most photographer work. Besides the big names in image editing, there are many others such as Paint Shop Pro, Gimp, Google Picasa, and of course the programs that camera companies offer or include with their camera bodies.
I use Ubuntu Linux, so it is a bit more challenging for me to find decent photography specific editing software. What I do currently is use an old license of Photoshop I own through a Windows emulation program called WINE. I also use programs such as F-Spot Photo Manager and RAW Studio.