Not only does BaiBoard allow students to collaborate on a shared whiteboard via their iPads, but they can also jointly annotate PDFs. Much like with AirSketch, BaiBoard also includes the ability to do a web share. This means that when on the same network, and with the unique URL associated with the iPad, ANY device can see a student working on their BaiBoard through a browser.
Touted as "the simplest way to make your own interactive eBook" this free program works on both Windows and Mac computers and is a great alternative to Apple's newly released iBooks Author.