Inkscape - Inkscape is a free, open source professional vector graphics editor for Windows, Mac OS X and Linux.
Xmind - Xmind is a brainstorming and mind mapping application.
Sketch - Professional digital design for Mac.
MindMeister - Create, share and collaboratively work on mind maps with MindMeister, the leading online mind mapping software. Includes apps for iPhone, iPad and Android.
Affinity Designer - Professional creative software, exclusively for Mac.
Coggle - Coggle is a simple, beautiful, powerful way of structuring information.