LastApp keeps track of the previously-used application and allows you to return to it. With this extension, you can quickly switch back-and-forth between two applications.

Once installed, you must choose an activation method via the Activator preferences pane in

If you have Backgrounder installed, you can optionally set the current application to background upon switching (unbackground via the normal Backgrounder method). This option can be enabled in the LastApp preferences pane in