In order to run MindNode, you will need a Mac running Mac OS X El Capitan 10.11 or newer. If you are still running OS X Yosemite, you can download version 2.3.5 from the Purchased tab of the App Store as long as you made a previous purchase. To view, or edit, your MindNode documents on an iPhone, iPod touch, or iPad, the device must be running iOS 9.0 or later with a copy of MindNode 4 for iOS installed.
With MindNode 2 for Mac we introduced a new file format. MindNode will read the older file format and ask you to upgrade to the new format.