iZooLu has announced Lock Desktop for Mac OS X (http://www.izoolu.com/wp/lock-desktop/). It requires Mac OS X 10.6.6 or higher and is available for US$0.99 at the Mac App Store in the Productivity category.
Once locked, the user can change user account or shutdown the computer. Applications and data continue to run safely in the background on the computer.
Additionally, Lock Desktop allows the user to switch between user accounts from the log-in screen while applications and data continue to run on the other desktops. It’s a single click solution.
