WordPress 3.4 will have a brand new theme in it – Twenty Twelve.

The initial version of which, has just been added to the development version of WordPress. The commit message explains the philosophy of Twenty Twelve:

Initial import of the Twenty Twelve theme, by Drew Strojny. This time around we’re trying something different than the previous twenty-something themes, a much more minimalist approach that affords easy use as a CMS in addition to being blog-forward. More information will be on wpdevel soon. Props drewstrojny and lancewillett.

Source: Trac Ticket #19978

I have set up a Twenty Twelve Demo Site here: http://twentytwelve.jamesc.id.au/

I’m very interested to see how it pans out!

Update: The Twenty Twelve Development Team has posted an update:

This is not yet a fully working theme — we’ll be adding in more features and lots of missing styles over the next 3–4 weeks. Including post formats, comments, archives and page templates, more in-post styling, and a nav menu rework so the main content comes ahead of the navigation.