Apps with 'Tree structure' feature

A hierarchical note taking application, featuring rich text and syntax highlighting, storing data in a single xml or sqlite file.

Workflowy lets you organise your brain into easily manageable lists. It also works as a single-pane outliner with inline notes. It offers one-click hoisting (zooming into branches). The online version syncs with mobile apps.

Manuskript is an open-source tool for writers, with outliner, character management, plot development, distraction-free editor, etc.

ToDoList is software in the category of Task Management, Project Management, Productivity, “Getting Things Done” (GTD), Scheduling, and Collaboration.

You can keep notebooks stored in plain-text and have them synchronized with a directory on your mobile device, SD card, Dropbox, or over WebDAV.

wikidPad is a Wiki-like notebook for storing your thoughts, ideas, todo lists, contacts, or anything else you can think of to write down. What makes wikidPad different from other notepad applications is the ease with which you can cross-link your information.

ACDSee is a complex, multi-purpose application that serves for viewing, organizing and editing digital photos. Furthermore, images can be shared on social websites or your own space on the developer’s website.

Manage your tabs and bookmarks in sidebar.

Next Generation Session, Windows, Tabs Manager and a TooManyTabs Solution That Really Works.

A new medium for your ideas—augment your thinking with a text editor designed for structuring lists. Side-by-side views allow 3 modes of thinking.

MyInfo is free form personal information manager- a reference-management system that allows you to collect, organize, edit, store, and find documents, notes, and project-support materials.

KeyNote NF is a flexible, multi-featured tabbed notebook, based on Windows standard RichEdit control. It's always accessible with a single keypress, even if you work in another application.

novelWriter is a Markdown-like text editor designed for writing novels and larger projects of many smaller plain text documents. It uses its own flavor of Markdown that supports a meta data syntax for comments, synopsis and cross-referencing between files.

A most awesome writing tool Create novels, short stories, research papers, notes.

The NERDTree is a file system explorer for the Vim editor. Using this plugin, users can visually browse complex directory hierarchies, quickly open files for reading or editing, and perform basic file system operations.