Chandler Project is an open source, standards-based personal information manager (PIM) built around small group collaboration and a core set of information management workflows modelled on Inbox usage patterns and David Allen's GTD methodology.
TiddlyWiki is a wiki that runs completely inside your web browser, without requiring a server (or even a web connection). It handles micro-content superbly and is great for managing stuff like your personal to-do lists.
Y. Cai, X. Dong, A. Halevy, J. Liu, and J. Madhavan. Proceedings of the 2005 ACM SIGMOD conference on Management of data, page 921--923. New York, NY, USA, ACM Press, (2005)