Deep Notes is described as 'simple hierarchical note pad. You can use it to outline ideas, make to-do lists, or whatever else might need jotting down in a list, hierarchical or not' and is a Note-taking Tool in the Office & Productivity category. There are more than 25 alternatives to Deep Notes for a variety of platforms, including Windows, Mac, iPhone, iPad and Linux. The best alternative is Microsoft OneNote, which is free. Other great apps like Deep Notes are CherryTree (Free, Open Source), NoteLedge (Freemium), WorkFlowy (Freemium) and Dynalist (Freemium).
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.
A professional list-making tool. Minimalist, keyboard-centric online outliner and task management application. Free sharing, unlimited lists, free import and export. Markdown and code support. Good for geeks 🤓 and keyboard lovers 💻.
NixNote, formerly Nevernote, is an open source client for Evernote . It is written in Java so it will also run on Windows & OS-X, but the primary focus has been to try and get a usable environment for Linux.