Present century is flooded with the mobile friendly generation. You hate to wait when your PC or laptop takes time to boot. You want it quick, you want it instantly, you want it at your fingertips and Drupal sites do come on your fingertips.
Drupal, an open and free content management system is designed considering the dynamics of the market trends. For the mobile friendly generation, Drupal has mobile friendly themes. Not just one or two or ten, the list is really long to be penned down. Herein, you can have a brief of some such themes.
Mobile
The Mobile Theme is used for clean and clear presentation of content on the mobile. Users can enjoy the same clarity which they enjoy on the screen of their computer systems. Further, this theme serves a dual purpose, on one hand it can be used on its own and on the other; it can be used as a base theme by enhancing the colors. In addition to the clear content view, the image display is adjusted as per the resolution of the mobile screen. The point to consider is that the image is neither compressed or expanded from the original view; the actual image in respect with the resolution of the screen is displayed.
Adaptivetheme Mobile
This is actually the subtheme for Adaptive Theme. This theme is best suited for small screen mobile and it provides 3 simple layout themes. However, it also provides support for iPhone’s apple touch icons. The foremost task of the Adaptivetheme Mobile is to strip out many of the additional and unwanted regions from the standard Adaptivetheme. Further, it undertakes the job of adding new layout as well as theme settings for the Access Keys (for both primary and secondary links). Simplified page.tpl.php and skip links for main content, search and primary links are yet few other key features of this theme.
Mobile jQuery Theme
Built on the jQuery Mobile platform, The Mobile jQuery Theme supports various mobile platforms. The A-grade platforms that have full enhanced experience with Ajax-based animated page transitions, the B-grade platforms without Ajax navigation features and C-grade that are basic, non-enhanced HTML experience still functional; are supported by this theme. The jquerymobile modules are used and enhanced for better functionality.
A-Cloudy-Day Mobile Theme
This theme is designed and developed for iPhones. The base of the theme comes from A Cloudy Day theme. From logo, to the slogan, mission, primary links, secondary link, search, user pictures and almost everything is supported by A Cloudy Day Mobile Theme.
Nokia Mobile Theme
As the name says it all, the theme specifically works for Nokia. However, owing to the key attributes, it also supports other popular devices such as iPhone, Android-based and Palm Pre/Pixi. The feature list further includes tweaks for touch screen and specific tweaks for specific Nokia devices like N900. The design of the theme gets its essence from official Nokia templates and the base of the theme comes from the original work of teemule.
There are many other themes and subthemes that support mobile web site. A few to name are Osmobi mobile theme, Mobile Ginkgo, Fusion Mobile, Community Media Theme and so on; the respective piece of work is not enough to list all.

