Mendely is a freely available reference manager and academic social network with web-based, desktop, and mobile versions; You can sync your library of papers between these different versions and across different computers.
UC Berkeley Mendeley users gain access to Mendeley Institutional Edition by accessing Mendeley via a UCB IP address. This gives UC Berkeley users 100GB personal library space, 100GB shared library space, 100 collaborators in private groups, and unlimited private groups. After leaving UC Berkeley, alumni will have access to Mendeley Institutional Edition for 12 months.
Non-UC Berkeley Mendeley users can still sign up for a free account, which offers 2GB of web space and the ability to create 1 private group with up to 3 members, or can upgrade to a premium plan to access more space or groups.
Reference managers (also called citation managers or bibliographic management software) offer a way to save, organize and manage references. Many work with word processing software to format in-text citations and bibliographies for papers and theses, allow you to share references, and enable you to attach or link PDFs to a citation record.
Wikipedia comparison of reference management software
New RefWorks / (Legacy RefWorks)