Although I have the Linux software mastering suite, JAMin , frequently I'll use Audacity and the accompanying LADSPA plugins (which also work in Windows) to master a song or album. Just import your favorite commercial production song (one that is a similar style to the song you are mastering) into Audacity, load your mixdown into the next stereo track for easy comparison, and tweak with the LADSPA plugins until they sound the same.
There are no presets for the LADSPA plugins, but once you have selected the ones that suit you best - and learned how they work - you can load in your own presets.

More good news: it's free... and being constantly upgraded


just looking for clues...
Oren.
http://www.masteringmatters.com