KeepNote is described by its author simply as
KeepNote is a note taking application that works on Windows, Linux, and MacOS X
KeepNote is started by creating a new notebook and then new page(s) within it. Each page can contain text of course, but images can be inserted (Edit—>Insert Image…) as well as screenshots (Edit—>Insert Screenshot…) and files (Edit—>Attach File…). For screenshots KeepNote Minimizes itself and in dragging the mouse one can choose a rectangular area for capture. Note that the aforementioned insertions work when in a page or when a page is visible or highlighted in the tree structure.