Tokyo Split Animator is a plugin for Final Cut Pro X that offers 19 split screen templates.  It allows you to animate-in and animate-out multiple clips; however, as you can see the above video, it also works quite well with multicam footage (something that works extremely well in FCP X) by easily allowing you to show all angles at once with a split screen animation.

Tokyo Split Animator is available through FX Factory for $49.  More details on Tokyo Split Animator’s website.