Padlet - Visual boards for organizing anything.
Freeplane - Freeplane is a powerful and free software for building mind maps.
BookWidgets - BookWidgets is an excellent application that let you create engaging exercises in minutes and easily share a varied variety of beautiful and fun activities with your classroom and others.
Linked Ideas - A macOS/iOS apps to treat ideas as links of concepts.
Quizalize - Quizalize is a leading web-based and mobile-based classroom application that delivers the best and easiest way to differentiates your teaching.
vym - VYM (View Your Mind) is a tool to generate and manipulate maps which show your thoughts.