TeenUp - A learning platform designed for teens by teens
Modelio - Modelio is an open source modeling tool supporting natively UML, BPMN and model exchange with XMI.
Alcamy - Free, open self-learning platform. Learn & teach anything.
Diagramo - Diagramo is an online flowchart software - diagrams (create, edit and share)
EduDo - EduDo is a video discussion platform
UML Designer - UML Designer provides a set of common diagrams to work with UML 2.5 models.