Von Trier and Leth's Five Obstructions

On the subject of variations, although more in the vein of abstract formal constraints, artist and cartoonist Deirdre Ruane drew my attention to a "diabolical game" that film makers Lars Von Trier and Jørgen Leth played with each other.

Leth, a major creative influence of Trier's, made a short film in the 1960s called The Perfect Human (Det perfekte menneske); Trier later challenged Leth to remake the film five times, each time within a specific set of formal boundaries: either each shot could be no longer than 12 frames, or the story had to be retold in cartoon form, or the remake had to be in a particular city.

The result, The Five Obstructions (De Fem benspænd), was a Sundance hit. There's a trailer on YouTube:

Unsurprisingly from that starting point there's little or no obstruction between you and the five short films.