Info at Miguel's blog ...
Every once in a while, people ask us "Will the Mono project implement WPF/XAML?" or "What is your position on Apollo?".
Some suggest that we must have a one-to-one implementation available in Mono. Some others believe that we should implement a new GUI toolkit and plot our own destiny.
Today we are announcing the response to Microsoft's WPF/XAML, a response to Flash and WPF/E. A cross-platform GUI toolkit (supports Windows, MacOS and Linux and is easily ported to new platforms) written entirely in managed code and 100% open source. It is completely licensed under the MIT X11 license terms as well, for your freedom-zero needs.
Screenshots here. This is likely to change *everything*.