Canvas 

The canvas area or the desktop area is commonly referred to as the “SmartCenter” and represents the foundation of the TouchSmart experience.  TouchSmart 4.0 runs as a full screen application, like all previous versions of TouchSmart.  Applications hosted within TouchSmart are displayed on the canvas.

Please note that this effectively changes the sandbox that your application is contained by.  Some applications may have display issues if they weren't built to resize dynamically, or to handle the sizes that are now possible.

Smartlets

Smartlets are new to 4.0 and allow users to drag different content “out” of your application and place it on the canvas.

You can now have content from your application 'pinned' to the canvas, providing yet another way to interact with your application.

Alerts

The alert system has been enhanced in TouchSmart 4.0 to include three different priority states.  In addition, more than one alert can be presented to a user on screen simultaneously.

The enhanced alerting mechanism allows you to better integrate your messaging into the TouchSmart shell.

Multi-Tasking

Applications are now run as needed, and not all at once on startup.  This greatly speeds up startup time and available resources within SmartCenter.

The user can also close applications without exiting the shell as needed in order to free up desktop space, clutter, and resources.