Collaborative tagging systems, or folksonomies, have the potential of becoming technological infrastructure to support knowledge management activities in an organization or a society. There are many challenges, however. This paper presents designs that enhance collaborative tagging systems to meet some key challenges: community identification, ontology generation, user and document recommendation. Design prototypes, evaluation methodology and selected preliminary results are presented. Categories and Subject Descriptors H.3.3 [Information Storage and Retrieval]: Information Search and Retrieval – information filtering, clustering. H.5.4 [Information Interfaces and Presentation]: Hypertext/Hypermedia - navigation. General Terms Algorithms, Management, Design, Theory. Keywords Collaborative tagging, collaborative filtering, link analysis.