Here's a few free minimal/clean Wordpress themes/frameworks that I have used on my blogs and love. These are perfect for creating simple and clean adult blogs that put focus on your content. I'm sure plenty of people here already have used or know about them but just incase anyone hasn't seen them, try them out on a few of your blogs and you might like them
Reverie
Reverie Framework is an extremely versatile HTML5 WordPress framework based on ZURB's Foundation, a powerful tool for building prototypes on any kind of devices. Reverie follows HTML5 Boilerplate standard and is hNews microformat ready. It is optimized for Search Engine while at the same time improve readability.
Roots Theme
Roots is a starting WordPress theme based on HTML5 Boilerplate & Bootstrap from Twitter.
Blaskan Theme
A forever free high quality theme focused on what WordPress does best: blogging. Blaskan is a responsive theme built for smartphones, tablets as well as laptop and desktop computers.
Bones Theme/Framework
HTML5 Theme and Wordpress framework
rtPanel Theme
rtPanel is a stripped-to-bone WordPress theme framework developed by rtCamp. It was known as ?rtBase? internally and over 300+ websites are already powered by rtPanel.