Are you looking for an alternative to your up to now favorite computer program XY?
The Web site AlternativeTo – “Find better Windows, Mac, Linux and online applications” could be a reasonable source for conveniently answering such question. At alternativeto.net you can search for the application that you want to replace. As result you will get a list of alternative software with similar (or even better) functionality. This list can then be filtered by tag, license (Open Source!) and supported platform.
AlternativeTo is run by the Swedish company 27 Kilobyte AB and online since March 2009. Searching is free. If you want to suggest a new application and to comment or vote for an existing one, you have to sign in via Facebook Connect or Open ID.
In case of my mission in finding suitable replacements for iTunes and Lightroom (yes, I am fed up of this “cool” Mac stuff), AlternativeTo brought me more useful candidates than an initial google search or sourceforge.net dig.
Yet it is far from complete and probably happy about your contribution.