Or is it also compatible with asp.net or asp.net mvc?
Check out this great post from Dave Ebbo: Link
WebMatrix is really a tooling story, that comes with a stack (IIS Express, SQL CE 4 and Razor) enabling you to create a new breed of ASP.NET page or site. Not only can you use WebMatrix to edit and maintain traditional ASPX pages (a la Forms or MVC), but you can use WebMatrix to edit PHP files, work with MySQL databases and manage PHP-based open-source apps (WordPress, Joomla, etc.)
Bottom line: inline with Razor is not the only option when using WebMatrix, though it is the default when creating new pages.