FREE PIMS offers almost two hundred free Personal Information Managers and the lists keeps growing. Also freeware in every Internet category possible plus a ton of webmaster tools and freebies.
J. Birnholtz, C. Gutwin, и K. Hawkey. GROUP '07: Proceedings of the 2007 international ACM conference on Conference on supporting group work, стр. 51--60. New York, NY, USA, ACM, (2007)