Expose is a sweet feature to switch applications if you have opened thounds windows in your desktop. In the FOSS territory, here are two competitors: Skippy and expocity.

Both of them are in portage. Personally, I prefer skippy since it is has less dependancies, only X and imlib2. The only drawback is the lack of fancy animation, and if you want to more advanced feature, like live snapshot, you need to do some hacks to enable composition of your X11 server. Here is a screenshot of skippy in action: