This is a fantastic alternative to Photoshop, and nearly as powerful. Was Mac-only till now, and was selected Apple's App of the Year. It's being released for Windows now, and they're giving away the Beta for free. The software normally costs $50.
You get RAW processing, HDR, layers, basically pretty much most of Photoshop and Lightroom's features.
Get the download
here.
Some more good info here.