Wiki Platform
SEAS hosts its own wiki platform called https://spaces.seas.harvard.edu, used by academic and administrative groups at SEAS for collaboration and sharing of ideas and documents.
For wikis related to courses please see https://wiki.harvard.edu
Source Code Repositories
See Version control.
Annotation Tools
Cool Collaborative PDF annotation tool : http://nb.mit.edu. Have your course PDF material on line, where students can enter notes, post questions and get answers!
Course Forums
Piazza is an online forum environment designed specifically for courses. It provides very rich control over registration (open or closed), student vs. instructor capabilities, web and email notifications, mobile apps, searching, tagging, response editing, and statistics. It takes only a few minutes for an instructor to set up a Piazza forum for a course.
For a tutorial see : http://www.slideshare.net/phsoffer/piazza-instructors-presentation
Web Conferencing for Teaching
http://elluminate.com