Classic WordPress Admin theme (prior 3.8 style).
Recently upgraded to WordPress 3.8+ and not yet ready for the visual change? WP Admin Classic plugin simply disables new admin theme and reenables the prior 3.8 looks to your admin panel. Please, note that there is still some unsolved issues (see "Issue list), so if you have ideas how to solve it just shout!
RTL Languages are not yet supported!!!
Post edit form turns blue (as a result for fixing http://1?ver=3.8 issue)
Admin bar is not displayed properly on front-end with standard Twenty Thirteen, Twenty Fourteen (updated themes).