Is there a software or plugin for video software that allows for arbitrary numbers and angles of split screens, and if so, what is it called?  

I.e. For a particular effect I wanted to split a screen in to 6 pieces the same way you would cut a pie. 

OR

I.e a non rectangular grid of split screens.

This kind of assumes there is a some kind of masking feature built in to allow non rectangular non 4:3 or non 16:9 screens.

I am targeting Windows 7 and 8 mostly, but if there is specific linux based video editor that fits the bill, don't hesitate to recommend it.