Shake 4 let you leverage the creative work you're producing in Final Cut Studio, extending it with an integrated workflow that put a wide range of tools e.g., sophisticated 3D multi-plane compositing, 32-bit Keylight and Primatte keying, cutting-edge Optical Flow image processing, smooth stabilization, image tracking, and an open, extensible scripting programat your fingertips.
MacRumors is reporting that the software has been removed from the Apple Store. The Shake webpage now simply redirects to the Final Cut Studio page.
Shake has been used in such films as Peter Jackson's The Lord of the Rings and King Kong, as well as Harry Potter movies and Cloverfield. It was also used by The Embassy to create a television advertisement for Citroën with a dancing car. Shake was used by Broadway Video for restoring the release of "Saturday Night Live: The Complete First Season" DVD box set. It is also in use by CBS Digital for creating new visual effects for Star Trek Remastered. [Wikipedia]
Rumors have surfaced in the past saying that Apple would replace Shake with a package, code-named "Phenomenon". However, there is no replacement product currently in sight.
If Shake is removed without a replacement this is likely to cause an upset in the professional community. Many pro users are already upset that Apple seems to forget the people that kept them alive and is now focusing more and more on the consumer market.