Apps to Hierarchical Tagging

Piggydb is an open-source web notebook application designed for building and managing knowledge bases, either individually or collaboratively. It emphasizes structured organization through hierarchical tagging and concept mapping.

Org-mode is a powerful and flexible mode for GNU Emacs, designed for note-taking, project planning, to-do list management, and authoring documents. It utilizes simple plain text files with intuitive markup.

DEVONthink is a powerful document and knowledge management application for macOS. It helps users organize, store, and retrieve information from various sources, offering advanced search capabilities, AI-assisted connections, and robust syncing options to build a comprehensive personal information or research database.

ToDoList is a robust, free task management software designed for individuals and teams seeking a highly customizable, tree-structured approach to project organization. It excels in breaking down complex projects into manageable subtasks, offering features like Gantt charts, Kanban boards, and extensive export options without requiring a web connection.

CintaNotes is a lightweight yet powerful note-taking application for Windows, excelling at capturing and organizing snippets of information quickly. Its focus on speed and hierarchical tagging makes it ideal for managing knowledge, research notes, and simple task lists effectively.