As a cross platform (Windows/Macintosh/Linux) solution, I would suggest Corel AfterShot Pro which is fast, compressive and responsive photo retouhing tool.
AfterShot Pro is not free but costs $99.99. Note that on time of writing this special offer with AfterShot Pro priced at $49.99 is available. Good thing is there is trial version available too so software can be checked prior buying.
Upgrade from different other re-touching software is available at moment of writing for $39.99 - To purchase the upgrade version of this product, you must own a previous licensed version of: Bibble Pro or Lite 5, Corel® Paint Shop Pro® Photo X2 or higher, Adobe® Lightroom® or Apple® Aperture®.

AfterShot Pro offers different presets and tools among others the usual:
- hue,
- luminance,
- contrast,
- exposure,
- saturation,
- highlights,
- sharpness,
- crop,
- rotate,
Worth mentioning software also has specialized presets/tools as Noise Ninja, a powerful noise reduction system and Perfectly Clear a kind of one button/action to adjust white balance, exposure, and contrast. In my opinion Noise ninja is a very good noise removal tool if not the best one I played with. Perfectly Clear is similar to auto function seen on different photo re-touching software (note that Aftershoot Pro offer auto color, auto level functions too) but it adjust several presets in one step, and often offers a great starting point for re-touching a photography, speeding up its development I found it very useful.
Update; Since Aftershoot Pro version 1.1.1.10 Noise Ninja was removed from software
System Requirements
Windows®:
Microsoft® Windows® 7, Windows Vista®, Windows XP with the latest service packs installed (32-bit or 64-bit editions)
Intel® Pentium® 4 or later or AMD Athlon™ 64 or later
2 GB RAM
250 MB hard drive space
Mouse or tablet
Minimum display resolution: 1024 x 600
CD-ROM drive
Macintosh®:
Mac OS® X 10.5, 10.6 or 10.7
All Intel® Mac® models are supported
2 GB RAM
250 MB of free hard drive space
Minimum display resolution: 1024 x 600
CD-ROM drive
Linux:
Fedora® Core 10 or Ubuntu® 8.04 or later (32-bit or 64-bit distributions)
Intel® Pentium® 4 or later or AMD Athlon™ 64 or later
2 GB RAM
250 MB of free hard drive space
Minimum display resolution: 1024 x 600
CD-ROM drive
Dependencies: GLib 2.4, KDE or GNOME recommended
Enable desktop compositing recommended
64-bit distributions require 32-bit compatibility libraries (ia32-libs)