X Timeline

I found an interesting collaboration tool for your students (and it's free). X timeline allows one or more people to create a comprehensive linked timeline covering any variety of subjects. The good thing is that the timelines can be shared online so you can create a timeline or research project that can be worked on collaboratively by more than one student.

Because the program is web sourced, you don't have to worry about students being forced to e-mail attachments back and forth to each other. Students can work on the project at home, or in the library before school, during lunch and afterschool. Students can work simultaneously communicating changes and revisions from two different computers.

http://www.xtimeline.com/
Here is the link. Search through the system for sample timelines