When it comes to taking notes, a simple text editor may do for some. However, Linux offers a wide range of specialized programs for this task, some of them shipping advanced features and powerful formatting and organizing tools.
Evernote is an service/application you can use to store notes, images and all kind of information (like audio, handwritten or video notes) for retrieving later.
BasKet This is one of my favorite KDE applications. BasKet is called by some a kill application for Linux, due to its completeness regarding features and a different approach compared to other notes applications.
Evernote is an application that allows users to collect, sort, tag and annotate notes and other miscellaneous information.