Sampa is not really a competitor of ASP.NET, PHP, Wordpress, DreamWeaver or anything that requires technical expertise. We are building a service for people to create rich websites (with blogs, albums, videos, etc.) without the need to any programming.
Still, this week I started working on the new Sampa.comwebsite (check out next week!) using ASP.NET 2.0. Boy, there are so many similarities between their new page structure and how Sampa works...
ASP.NET: Themes vs. Sampa: Master Templates -- both define the basic style elements (color, fonts, backgrounds, etc.)
ASP.NET: Master Pages vs. Sampa: Page Layouts -- Defines the "wireframe" structure of the page and some fixed content (header, footer, menu, etc.)
ASP.NET: Controls vs. Sampa: Content Boxes -- Dynamic generated content.
ASP.NET: Pages vs. Sampa: Pages/Web Modules -- The "main content" of the page.
Now, ASP.NET lacks one more level of flexibility that Sampa has: Box Layouts. Basically, if you go to the Master Page on your ASP.NET app, you can only say where the region is, but you can't say what happens if the region is empty. That is important because on certain cases you want to suppress some HTML outside of a region if it has nothing on it. On Sampa, Box Layouts are only displayed if the content inside them is not empty, and you can change the Box Layout very easily.
BTW, this Site is using Sampa. See the box on the right where it says "About Me". It has two parts to it: The text inside it and the layout surrounding it (the Box Layout). There is no similar on ASP.NET (although you could hack it).