Web 2.0 has created new applications with remarkable socializing nuance, such as the SBS (So-cial Bookmarking Systems). Rather than focusing on the relationship between users, the SBS provide users with the necessary tools to manage and use information that can later be shared.
This article presents a description, analysis, and comparison of different SBS, which are catego-rized as web applications that help to store, classify, organize, describe, and share multi-format information through links to interesting web sites, blogs, pictures, wikis, videos and podcasts. Also emphasized are the advantages for learning and collaborative research that SBS produce.
In this paper, Diigo will be specifically studied for its contribution as a metacognitive tool. Diigo shows the way each user learns, thinks, and develops the knowledge that was obtained from the information previously selected, organized, and categorized. Thus, the information becomes high-ly valuable, and knowledge is cooperatively built. This knowledge induces collaborative learning and research, since the tags that describe marked resources are shared between users. Conse-quently, they become meaningful learning resources that provide a social dimension to both learning and online research processes.