Established way back in the days of the Nokia 7650 was that if you wanted to access the list of running applications in the multitasking OS, you long pressed the 'menu'/'apps' key - and the system hasn't changed in ten years. But it does involve you finding and pressing a physical key and, worse, having to wait a second with the button down, to qualify as a 'long press'. Tsk Switch, in the Nokia Store, gives you access to the same multitasking carousel with a single screen tap, for example from your homescreen.
It should be noted that Nokia itself tried something similar by putting 'show open apps' at the top of every application menu, but this involved you having to bring up the menu each time and then step up and select the option, all of which took more time than long pressing 'menu'/'apps'.
Here's Tsk Switch in action:
(Left) as the message suggests, a one-time message to let you know the application is now ready for action; (right) in (for example) a homescreen shortcut slot, you can pick Tsk Switch as the assignment.
(Left) Tsk Switch on a homescreen; (right) tap it and you're immediately in the multitasking carousel!