If you lust after Adobe Lightroom but are not keen to lay out the $149 that Adobe is asking for the version 5 software then there's a free open source project that you just have to check out called LightZone.
Here's a description of the product:
LightZone is professional-level digital darkroom software for Windows, Mac OS X, and Linux. Rather than using layers as many other photo editors do, LightZone lets the user build up a stack of tools which can be rearranged, turned off and on, and removed from the stack. It's a non-destructive editor, where any of the tools can be re-adjusted or modified later - even in a different editing session. A tool stack can be copied to a batch of photos at one time. LightZone operates in a 16-bit linear color space with the wide gamut of ProPhoto RGB.
While many of LightZone's tools are standard fare, it offers some unusual ones for tonal control - meaning brightness, contrast, shadows, highlights, etc. Some are inspired by the Zone System, and some are inspired by HDR tone-mapping. These tools put LightZone in a class by itself for working with black-and-white imagery. They're useful for color photos, too.
LightZone was a product developed and sold by a company called Light Crafts which went out of business in 2011 leaving a sizable community of enthusiastic users potentially high-and-dry. At the end of 2011 my list-friend, Doug Pardee, along with Anton Kast (one of the original authors of LightZone) and William "tex" Andrews persuaded Light Crafts to turn the software loose.
The original goal of The LightZombie Project was to just keep the software working and they apparently didn't see going open source as a real possibility. Then late last year Fabio Riccardi, the original proprietor of Light Crafts, agreed to release the source code under a BSD license.
Much to the founders surprise, a bunch of developers then stepped up and by last Christmas the software had been seriously polished and the project was renamed The LightZone Project. Since then the code has been released on GitHub and versions for Windows, OS X, and Linux have gone to beta.
Along with that the project has seen an explosion of interest with the registered user population expanding rapidly from a few hundred prior to early July this year to almost 3,000 by July 15 and as of a week ago it was increasing by about 500 users every day!
The LightZone Project shows not only how powerful open source is in getting people to work together when they really care about a way of working but also why when companies decide to, or have to, stop selling software they should give their code away rather than just bin it.