Document Node 1.5.1 for Mac was available to download from the developer's website when we last checked. We cannot confirm if there is a free download of this app available. We recommend checking the downloaded files with any free antivirus. This free Mac application was originally designed by Document Node Pty Ltd. Document Node for Mac is included in Productivity Tools.
From the developer:
Document Node is a lightweight application, where you can arrange your Markdown or Rich Text content in a flexible local folder structure (notes taking), review and modify your document in a Mind Map view, and export documents in various formats. All documents sit in your local folders, so the privacy of information is preserved.
You may want to check out more software for Mac, such as Node.js, Spot Documents or OnTheAir Node, which might be similar to Document Node.