We love Macaw, and the early preview looks amazing! Can't wait to play with the final version. That said, it looks like it is much more similar to Adobe Edge Reflow, but with a more intuitive interface.
With Webflow, we're looking to build a more comprehensive hosted platform that allows designers to create production websites and actually deploy them live. Down the line, this means that content management, functional web forms, eCommerce integration, and a variety of other things are possible out of the box, without the need to export code and change it manually. Even simple things for programmers like script compression/concatenation and CDN acceleration (all of which happen after the design phase) are hard for many designers to set up, so we want to take as many headaches away as possible so designers can get back to work.