Wrath of the Mountain King is an adventure with an old-school flavor. It will be a 35 page d20 adventure module for 4-8 characters of levels 2-4, and it will be released under the Open Gaming License, meaning that you can play it using the System Reference Document released in conjunction with D&D version 3.5 and available at the Wizards of the Coast website.
Wrath of the Mountain King will be released in August 27th.