Automattic have introduced Toolbox Theme for WordPress a saemantic, HTML5, canvas for CSS artists and an ultra-minimal set of super-clean templates for your own WordPress theme development.
“Much like the Sandbox theme, Toolbox provides all the markup you need to build your very own theme with CSS alone–with one difference. Toolbox uses some really exciting new HTML5 elements–like article, header, and nav–that better describe what your content is all about.”
Automattic Inc. is the startup company behind WordPress and other projects.
More info: http://en.blog.wordpress.com/2010/12/10/new-theme-toolbox/