Every now and again I get asked what framework I use when implementing designs into Drupal. If you aren't savvy with the term framework; a framework is simply a blank canvas in which certain aspects and elements are built in their own respective ways (usually grids) for a 'blueprint' or 'mockup' to be developed on top of.
Over the past years Drupal has been slowly clawing it's way to the surface to show it's true place as number one in content management systems and in saying so; developers around the globe have straught to bring many excellent elements for ease of use with Drupal. Now, let's get to the beef of the top 3 frameworks I personally recommend for Drupal.
If you're a CSS developer then you've bound to have heard about Zen somehow. This excellent blank HTML5 starter theme is perfect for when you need to develop a quick broshure site or even a small informational splash page.
Zen is reponsive and built on a mobile-first grid design. Setting up a sub-theme is quick and painless and can get your project started almost immediately. Zen comes equipped with Sass/Compass ready documents as well as nice features like HTML5 shiv, respond.js and of course the aforementioned responsive design. To see a full list of features visit: https://www.drupal.org/project/zen
Bootstrap is incredible, there's no doubt about it. Equipped with responsive design, lucious premade css eye candy, HTML5 and the whole kit & caboodle. You seriously can't go wrong when choosing bootstrap to start your project whether it's a large or tiny site.
It's a little more advanced to get started with in regards to Zen and has a requirement of jquery 1.9+ but once ready to get moving you can really appreciate all the nice features this framework comes equipped with. To see a full list of features visit: https://www.drupal.org/project/bootstrap
Coming to the number one spot here is AdaptiveTheme. Some may argue that bootstrap should be placed here but in my honest opinion, I personally feel AdaptiveTheme is the most powerful framework out of the other two in regards to speed & accessability and even the features are on par with all modern frameworks these days.
It just down right feels perfect with Drupal especially with augmentations of panels, display suite and a few other modules you can seriously turn your site into a monstrosity. To see a full list of features visit: https://www.drupal.org/project/adaptivetheme
That about wraps it up for the three frameworks that seem to be taking charge for Drupal at the moment. I personally gave you my order of the three but in regards they're all powerful frameworks in their respective areas and can even outshine some in others through various things.