Open Source Apps with 'Hierarchical structure' feature for Android
- An open source note taking and to-do application with synchronisation capabilities.
- TagSpaces is an open source personal data manager.It helps you organize and browse your files on every platform.Cross-platform file tagging and file finding
- An org-mode file viewer for iOS and Android. Imagine a plain-text markup language like Markdown, but married to an application that is a literate programming environment and life organizer.