ChronoZoom, a good tool for creating multilayer timelines, is shutting down on March 15th. Roland Saekow, ChronoZoom's co-founder, announced the closure through an email sent to ChronoZoom users. In the email Seakow announced that public projects will be archived and made available for download. Directions for making your projects public can be found in this Google Document.
ChronoZoom was a great tool for making timelines that displayed multiple layers so that viewers can see how events and eras overlap. If you're looking for another tool that can be used in that way, try Timeline JS.