Sheldon J Pacotti, writer of Deus Ex, has released a videogame creation tool called Game Blocks. John Walker at Rock, Paper, Shotgun:
Described as “a free library of visual programming ‘blocks’ for first-time game developers,” Game Blocks is the result of something Pacotti built for an interactive writing course he teaches at the University of Texas. The idea being to encourage others to create non-linear storytelling in games. It’s a visually simple tool, based on BYOB, that lets you construct scenes without being stuck in a linear path, as well as include simple physics, and even platforming.
Pacotti tells me, “They are meant to provide the simplest possible environment for constructing non-linear stories, which in my mind comprise more than talk trees and branching conversations. My students typically add mini-games, puzzles, and even arcade-like interactions to their projects, all of which can convey story.”
Game Blocks wouldn't even be a bad screenwriting tool, it might even suit someone like Charlie Kaufman . Here is a demo of GB: