Freeplane - Freeplane is a powerful and free software for building mind maps.
UXpin - Design is really about solving problems. UXPin is the UX Design Platform that gets that right.
Linked Ideas - A macOS/iOS apps to treat ideas as links of concepts.
Figma - Team-based interface design, Figma lets you collaborate on designs in real time.
OmniOutliner - OmniOutliner is a writing app for collecting information, outlining ideas, adding structure to any sort of writing.
Moqups - The most stunning HTML5 app for creating resolution-independent SVG mockups, wireframes & interactive prototypes for your next project