Freeplane - Freeplane is a powerful and free software for building mind maps.
Teachable - Create and sell beautiful online courses with the platform used by the best online entrepreneurs to sell $100m+ to over 4 million students worldwide.
vym - VYM (View Your Mind) is a tool to generate and manipulate maps which show your thoughts.
Clever - syncing between education applications for K-12 schools
Linked Ideas - A macOS/iOS apps to treat ideas as links of concepts.
Claroline - Claroline is a collaborative eLearning and eWorking platform.