Regarding timeline apps, I did some checking and I’m surprised how few there are that let you build your own timeline. One of the reasons we advocate creating a book of centuries (basically a timeline in a book) is that it helps the student form his own connections to the history. A pre-made timeline app doesn’t do that because it only spoon feeds you pre-made facts.
The Knowledge Quest app already mentioned is one that lets you create your own timeline. I haven’t personally tried it so I would love to hear from those who have or are aware of other apps that let you create your own.