Google Docs allows for real-time collaboration on everything from documents to spreadsheets to presentations, while also allowing for individuals to edit and others to view. You can share documents, folders, and almost anything else you create in Google docs.
Skype allows for students, faculty, and staff who are abroad, off-campus, or even in different buildings to video-conference and work in real time on projects, assignments, or research. Librarians have used Skype to conduct research consultations with students who are unable to be on campus and need more direct help than chat can provide, and can be used for advising meetings, writing help, and other collaborative projects.
Join.me allows for faculty and instructors to share their screen. Faculty have used this to help students on projects and research papers, and it is used by Fortune 500 companies for conference calls and meetings.