Lean PD

Truly Simple Timeline was built by a professional author to help keep track of narrative arcs, story beats, and which characters participate scenes across the span of a novel.
It’s customizable to make it useful for all sorts of purposes, though, and its visual, drag-and-drop interface and cross-device functionality makes blocking-out events across centuries or the hours in a single day (and then adjusting those events later, as things progress) easy.
There’s an in-app purchase that allows for an unlimited number of timelines, but all other features are available in free version.
Features:
• Intuitive drag-and-drop interface
• Large-scale arc events (for delineating acts or other macro-scale periods), single-date events, and duration events with beginning and end dates
• Add events one at a time, or add batches of them all at once
• Vertical and horizontal modes on both iOS and MacOS
• All features available for free (paid ‘pro’ version unlocks ability to have more than one timeline going at once)