MyTetra (Version: 1.30 tested) is an open source and cross platform note taker, notes organizer or PIM. It doesn’t have the most modern interface but it is a good option if looking for an organizer.
MyTetra is tree structured. Its structure is item (or sub item) with separate note(s) within each item or sub item (see image). It comes with a base item and sub items or siblings or other items can be added. MyTetra has an unusual characteristic, it requires each item to be divided into notes, the nodes in the tree themselves don’t hold any text, just a