First one is ActionOutline. It comes in 3 versions – Free (lite), Standard ($39.95), and Pro ($79.95). Pro can be used to share docs in a network while Standard is stand alone.
Instead of the file/folder format of MS OneNote, ActionOutline (and TheGuide as well) use the tree format – which is also useful.
Second is TheGuide. This one is free.. and has basically the same functionality as the Standard version of ActionOutline has. So, I would go with this one. Rather interestingly, it also provides support for a number of languages – like Malayalam, Hindi, Tamil, Greek, Arabic, Sanskrit, Russian, Chinese, Japanese, Kannada. So you can choose in what language you want to write your notes.
How can it be used? You can give a structure to any “project” – IT project, Home assignment a novel, research paper, Book list, list of recipes, travel itinerary or business proposal – and then fill in the information you want.
I haven’t tried these two myself so I cannot talk about their performance, but from the look of it and because it is free, I will definitely try TheGuide!