BlackMesa is a free theme for WordPress created by Arcance.
A graphically intense theme with alternating, semitransparent headline-boxes, parallax moving backgrounds and beautiful text styles. Supports featured thumbnails, custom headers, custom menus and multiple widget areas.
(Description "BlackMesa" Theme from wordpress.org)
You can download BlackMesa for free via the provided download link and include it into your themes folder of your WordPress installation. Also you can directly search for it in the WordPress admin interface in the themes section and install and activate it from there.
More information, screenshots and reviews of BlackMesa Theme can be found here.