The name of the software is Zettlr, a markdown editor optimized for academic long form writing.

The homepage can be found here: https://www.zettlr.com/

Unlike the other markdown editors in the repository, this one allows for folding, thereby enabling almost outliner-like navigation and review of longer pieces of writing. Based on Electron, it is also much leaner and faster than Atom.

It is open source.

I hope this is an adequate link to the github download: https://github.com/Zettlr/Zettlr.git