We use the reset of all resets by Eric Meyer. Some nice typograhical styles working off a consistent vertical rythym. As well as some simple button styles.
With these powerful classes you can quickly build slick interfaces while writing a lot less code. Remember, these are open for extension; not modification.
Bare-bones sample module pattern to keep your JS nicely organised. Bootstrapped with jQuery, but vanilla enough to adapt to your preferred library.
Everyone builds websites in their own way. Groundwork doesn't come with a grid system or any other packaged modules. Easily import more stylesheets when need be.