Twitter is a free social networking and microblogging service that enables it's users to send and read messages known as tweets. Tweets are text based posts less than 140 characters
Facebook is a social networking site that allows users to add friends and send them messages and update their personal profiles. Additionally, users can join networks organized by city, workplace, school or common interest.
YouTube is a video sharing website on which users can upload and share videos.
The CSUN Alumni network is a social networking service that enables CSUN Alumni to interact and share with other Alumni.
LinkedIn is a business oriented social networking site.