Lineal is an iPad App for making timelines that I created in 2011 with Brian Jacobs, Duncan Malashock, and Colleen Clery. You can view events on the scale of millenia, or zoom all the way in to minutes. Events can be tagged and filtered, and arrange themselves into scrollable 'stacks' on top of dates.
You can scroll smoothly along even the most densely populated timelines, zooming in and out to gain perspective.
Lineal still has a core group of loyal users. Beta testing is in progress for an update to the app that will bring some often requested features.