Dropbox is already used by millions of students and teachers. ( 2011 Forbes article about Dropbox in the classroom: http://onforb.es/oDUIj1 )
DropLearn (the startup formerly known as OneSchool: http://tcrn.ch/x2ZcX4 ) is building iOS and Mac apps built exclusively on top of Dropbox.
DropNote -- Simple app for notes, assignments and calendars.
DropClass & DropTeach -- Mint.com for learning management systems (LMS).
DropLearn -- Learning search, discovery and dashboard for online courses.