C#/XAML for HTML5 new Beta 10.0
cshtml5.com
cshtml5.com
I could also see a case made that XAML has an arguably much cleaner layout system and styling system than HTML, so some developers may prefer it to HTML.
To develop cross-platform code (e.g. for desktop and web targets)?
Stating that some language is better than another isn't really a good argument, most of it has to do with domain specific knowledge being leveraged to enter another market.
If it's commercial the lack of any pricing or licensing information leads me to want to avoid at all costs... I'm assuming it's a commercial product, and it's completely not clear short of giving your email address to download.
This project is obviously still in development. You can see their roadmap almost on the bottom of the main page [1].
Around 2010 when I was a WPF dev moving back to web I looked so hard for a tool that would do this.
I'm guessing this renders as SVG but CSS (mainly flexbox) and tools have improved so much that it's not needed so much now.
Still going to have a good look into it though.