Most comprehensive but also expensive high fidelity wireframe and prototyping tool used by professionals.
UI/UX planning suite to wireframe user interfaces, create user flows, document styles and approve designs.
Flows & Charts
Super simple tool to create wireframes, flowcharts, sticky notes and mindmaps and then collaborate on them.
They have all kinds of diagramms and charts ready to customize or you just start creating your own from scratch for free.
UserBit helps to understand user needs, manage interview notes, synthesize data, create personas, visual sitemaps and more.
Useful UX Helper
Laws of UX
Laws of UX is a collection of the maxims and principles that designers can consider when building user interfaces.