yeah but it is prolly the worst one out. Third party apps have the advantage because that is all they are designing it to do. They are faster and better. Diskeeper for example can defrag a 200GB HD in about 30 mins or less and it will be completely free of fragments. However, Windows' defrag util takes a lot longer and doesn't completely defrag the drive. That is because it will not move whole files around to make them fit better. I think Diskeeper is worth the investment. I have it set up to defrag my computer every week at night and I have never noticed a problem and my HD is always at 0% fragments.
-Aaron
*edit*
Also I forgot this but most third party progs will also touch system and page files. Microsoft wouldn't dare to do that.