LucidChart is a free tool for educators that allows the creation of collaborative flow charts and diagrams. This would be a great tool for any language arts, social studies, or other class where writing/pre-writing activities are done in visual form. It would also be helpful to help display events in series, visually map a complex process, etc.
Have a look at the tool in action, as it is used to map the lyrics to The Beatles’ “Hey Jude”:
LucidChart is generally a paid-subscription service. However, LucidChart for Education is offered free-of-charge for teachers and students at this link.