Perilous Intersections

From the introduction:

Perilous Intersections is a lightweight engine to power your solitaire roleplaying game adventures. It works by directing you to answer the Big Questions that brings a hero into conflict with a setting’s threat. It keeps some measure of surprise while the emergent plot provides resistance to the protagonist’s motivations. It works best with characters that have strong motivations and are action-driven. It can work in tandem with any existing RPG system, and is interactive, responding to the PC’s efforts to counter the main antagonist, making her choices matter.