A great comparison of available genealogy software can be found on... Wikipedia. That's right, the world's largest encyclopedia contains comparisons of genealogy products, including both free and commercial programs. Software compared includes Windows, Macintosh, Linux, and web-based products.
The Wikipedia article begins at http://en.wikipedia.org/wiki/Genealogy_software and then you can scroll down the page to find links to a comparison of genealogy software installed locally on personal computers and to a comparison of web-based genealogy software. Explanation of many terms, including GEDCOM,are also available in the article or in articles linked to the article.