Why summize when the official MasterView site has the best explanation I can find?

MasterView™ is a ruby/rails optimized HTML/XHTML friendly template engine. It is designed to use the full power and productivity of rails including layouts, partials, and rails html helpers while still being editable/styleable in a WYSIWYG HTML editor.

MasterView allows you to write HTML in a somewhat normal way for an entire page (that is, one page within a single HTML file) along with specialized attributes which MasterView can then use to convert that HTML file into a set of Rails-friendly views and partials. The fully zoomed version of the screenshot on this post provides a good demonstration. The Masterview site also provides some screencasts to show how to get things going.

Yet another interesting Rails templating option!