I have read very interesting list of Knowledge visualization tools. Read both the post and comments. They can be used when you carry on research.
An excerpt from the blog
* Storage of notes and documents
* Search functionality and keyword/tagging capability
* Outline view in a traditional hierarchy, or user-defined views
* Task management, calendar, and contact management (mainly PIM, not KM)
These are essential features, however don’t offer too much to the more visually-inclined knowledge junkies. For visual learners and information visualization fans, having a graphical representation of knowledge and seeing how things relate is a must have feature. Luckily, in the past few years there has been a rise in the number of knowledge management applications that offer this capability. The following is a list of interesting /unique / effective tools for knowledge management and information visualization (not listed in any particular order):