CUSTOM SPLIT SCREEN TOOL FOR FINAL CUT PRO X
Bronx Blocks for Final Cut Pro X from Brooklyn Effects

http://brooklyneffects.com/

Bronx Blocks was designed by Brooklyn Effects™ to be the most intuitive, and customizable split screen effect for FCPX. Simply stack your media in the timeline; drag and drop a shape effects on top of each layer, and use the built-in control panel to change the position.