FreeMind - FreeMind is a premier free mind-mapping software written in Java.
Arguman - Structured debating platform that allows you to flag fallacies
XMind - XMind is a brainstorming and mind mapping application.
Kialo - Kialo is the platform for rational debate. Empowering reason through friendly and open discussions.
MindMeister - Create, share and collaboratively work on mind maps with MindMeister, the leading online mind mapping software. Includes apps for iPhone, iPad and Android.
argunet editor - Argunet Editor is a free argument map editor for analyzing and visualizing complex debates.