What is Mendeley?
Mendeley helps manage and share academic knowledge: Mendeley Desktop is free academic software (Windows, Mac, Linux) for organizing and sharing research papers and generating bibliographies with 1GB of free online storage to automatically back up and synchronize your library across desktop, web and mobile. Mendeley Web is a free research network which lets you manage research papers online, discover trends and connect to like-minded academics. Mendeley tracks usage data on over 40 million research papers in real-time, thus creating a network of people using and sharing millions of scholarly articles - helping to shift research into the 21st century world of collaboration and openness. Mendeley is engendering a revolution in the way research is conducted and disseminated, changing the face of science.
With Mendeley you can view and annotate PDF files. The PDF exported along with the comments can be readily viewed in Adobe's Reader.