Freshdesk - Freshdesk is a cloud-based customer support software that lets you support customers through traditional channels like phone and email, social channels like Facebook and Twitter, and your own branded community
draw.io - Online diagramming application
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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.
Zendesk - Zendesk is a beautiful, lightweight help-desk solution.
PlantUML - PlantUML is an open-source tool that uses simple textual descriptions to draw UML diagrams.