Command + Tab for Trackpad?

Some trackpads can do application switching, some older ones cannot. (For instance, the Magic Trackpad I use with my Mac Pro can, but the trackpad on my circa 2006 MacBook Pro cannot.)

The specific gesture currently set to do it on your Mac should be in System Preferences > Trackpad. If that shows only one- and two-finger gesture settings, your trackpad is too old to detect three- and four-finger gestures. (My six-year-old MacBook Pro trackpad falls into that category.)

I'm assuming you are using Lion, since you posted in the Lion forum.

In Snow Leopard, a 4-finger swipe on the Trackpad would reveal the application switcher (the row of app icons you get with command-tab).

This feature was removed with Lion and Mountain Lion.

The only way to get it back is to use a 3rd party tool like 'BetterTouchTool'. Click the top left icon on this page:

http://blog.boastr.net

and it will download. The tool is currently free.

(Disclaimer: I am not connected with the developer in any way whatsoever)

You're welcome.

You might need to experiment with the settings. In fact, due to Lion getting a bit confused about what the swipe gesture is supposed to do (even if you deactivate swapping desktops), I found that a three-finger tap works far more effectively and reliably, but you can define your own gestures in BetterTouchTool, whatever works best for you.