My Mind by Ondřej Žára.
From the webpage:
My Mind is a web application for creating and managing Mind maps. It is free to use and you can fork its source code. It is distributed under the terms of the MIT license.
Be sure to check out the Mind map features version. (Check out the documentation for basic commands.)
I first saw this in Nat Torkington’s Four short links: 22 January 2014.