Based on xkcd's comic about the subject, this page is for when you're not sure what measure of average you should take, so it uses the best of both worlds by calculating all three of the arithmetic mean, geometric mean, and median... then repeating the process on those repeatedly until they converge to a single value. Note that this usually doesn't play well with non-positive numbers.
As a bonus, this page also provides the option to change what is included: