The Mac has something similar called Screen Sharing but its not nearly as popular or as in demand as RDC.
The mechanics of this desktop sharing is built into every PC and essentially it allows a remote computer to connect and manipulate the desktop of another. Its very handy in the support field but it is also pretty good if you want to work from home.
Imagine this, as unpleasant as it might be, that you have Windows at work but a Mac at home. If you have been granted access to the work network from your home Mac Microsofts Remote Desktop Connection application (free download) for Mac has always been available.
Well truth be know there have been many RDP apps out for the iPad and iPhone but they have all been limited or costly.
Now, at last, Microsoft have produced their own version and its free, stable and easy to use. Its the only one you need to worry about if you want to control your Windows desktop using your iPad or iPhone.