From iPhone Development Wiki

Multifl0w is the first task switcher to show application snapshots. The goal was to create a more visually pleasing switcher than Kirikae, and to give the iPhone something more on-par with other smart phones.

Multifl0w was created by Charybdis and released on November 22, 2009.

The program is a dynamic library that hooks into Springboard using Mobile Substrate. A screenshot is taken using takeScreenshot, a function added to SpringBoard which takes a snapshot using UIGetScreenImage(). Screenshots are added and removed from an array as necessary, as well as the application identifiers for the screenshot.

Multifl0w adds the void function 'invokemultiflow' to SpringBoard, which opens the Multifl0w interface. If you would like to write a custom method for opening the interface, the following code should get the SpringBoard, and call invokemultiflow to bring up the interface.

	SpringBoard *springBoard = (SpringBoard *)[objc_getClass("SpringBoard") sharedApplication];
	[springBoard invokemultiflow];

And the following will close Multifl0w:

	[springBoard dismissmultiflow];

The official website for multifl0w is here - [1].