I am not sure there is such a thing as "knowledge management." The concept seems incoherent to me. However, there are interesting applications that allow one to manage one's notes and ideas.
In a very interesting post, Eric Blue presents what he calls: 15 Effective Tools for Visual Knowledge Management. It's worth a look.
The link comes to you thanks to Franz Grieser and the Outliner Forum.
I should perhaps also point out that my favorite note manager is regrettably not included. Too bad.