ofCourseBooks - Let your students write, save and share their course notes.
Trustroots - Travellers community for sharing, hosting and getting people together.
Teech - 24/7 Unlimited help from the world's best students
BeWelcome - Open your door to the world!
GitHub Student Developer Pack - The best developer tools, free for students.
Hospitality Club - Free network of people around the world who offer free accommodation, advice and help when they are traveling - hospitality exchange. Free membership.