TeenUp - A learning platform designed for teens by teens
draw.io - Online diagramming application
Alcamy - Free, open self-learning platform. Learn & teach anything.
LucidChart - LucidChart is the missing link in online productivity suites. LucidChart allows users to create, collaborate on, and publish attractive flowcharts and other diagrams from a web browser.
EduDo - EduDo is a video discussion platform
PlantUML - PlantUML is an open-source tool that uses simple textual descriptions to draw UML diagrams.