Simplest way to create busy animation in WPF

I mentioned that there is no standard busy control in WPF. So what's the easiest way to display animated busy circle (not progress bar) such as your browser displays when loading a page ?

Please if you suggest downloading control from internet make sure that this control is for free and with no licence restriction (such as I would be forced to GPL my application if I use it).

Thank you in advance

Does WPF support animation?

WPF provides builtin support for animations. The WPF animation system makes it very easy to animate controls and other graphical objects.

Is WPF fast?

In general, WPF is perfoming much worse in drawing performance than Windows Forms, and native GDI or DirectX. Yes, WPF is powerful in the sense you might make some neat stuff that is not supported in GDI, but it is more sluggish.

There's also Sacha Barber's Circular Progress Bar. It's licensed under the Code Project Open License.