Each scene is a .js file. You set how many steps it has and use CSS classes to say what shows up at each step. Going back, skipping or replaying a step always lands on the same visual state.
The presenter view opens in a second window, synced with the projection, with the notes for each step, the next step, a timer and a clock. The PDF comes out with one page per step. The deck makes no requests outside your machine, so it works offline.
The demo is a real class from my mentorship's Dojo, "Como uma empresa de fora lê o seu CV" (how a company abroad reads your CV), in Portuguese. Press P to open the presenter view. It is for people who want to write slides as code and present straight from the browser.