Freeplane began as a fork of the Freemind project. While maintaining comparability with Freemind file format, it has far outpaced in features and development. As of 3/5/2022, the latest Freeplane update (1.9.3) is 3/5/2022 vs Freemind was last updated (1.0.1) 2/5/2016. Active, helpful community.
UXpin - Design is really about solving problems. UXPin is the UX Design Platform that gets that right.
Xmind - Xmind is a brainstorming and mind mapping application.
Moqups - The most stunning HTML5 app for creating resolution-independent SVG mockups, wireframes & interactive prototypes for your next project
FreeMind - FreeMind is a premier free mind-mapping software written in Java.
Axure RP - The prototyping and specification software used by 87% of the Fortune 100. Beyond mockups, design interactive prototypes for business solutions, websites, and applications.
Linked Ideas - A macOS/iOS apps to treat ideas as links of concepts.