Draw.io is free, high quality diagramming application. It can be used as a designing tool for storyboarding, creating flowcharts, network designing etc in classroom.
Flowdock can be used by teaching teams for conversations, sharing ideas and tools within their team, across the organization or to collaborate with educators across the globe. Prioritize work, solve problems, search and organize across teams, locations and timezones. Its a tool to provide real-time team chat for your entire organization.
Flowdock can also be used to connect with students outside lessons. Send them reminders about assignments, time table, extra classes and submission dates.