An engine to express game mechanics as algebraic properties. The primitives enable exploring statistics, optimizations and simulations.

An "Any Gate" generator that ingests a sourcebook and creates a Baldur's Gate-like experience. Backgrounds, character portraits, items, and the like are generative or crowdsourced.

A screenwriting program for graphic novels that makes it easy to lay out the panels themselves, along with speech bubbles and skeletal storyboards.

An AI with no knowledge of how a historical event played out, for use to predict the consequences of other-than-actual decisions during that event.

I think famous battles would be a good use for this.