Timelines, much like calendars, can be used to show changes over time in a straightforward way. When you have a bunch of events that occurred at certain times, mark them on a timeline, and you quickly get a sense of what's going on. Take the timeline of 10 largest data breaches for example. You see breaches get more dense as time goes by.
Wrap this idea into web application form, and you get Dippity. There have been similar timeline applications, but Dippity does it a bit better with a primary focus on telling stories with timelines and a good interface. Zoom in, zoom out, drag, and get alternative views as flipbook, list, and map.
Below is a little bit of context to my gas price chart. Check out the full version for a better idea of what Dippity offers.