RingCentral - RingCentral is the leading provider of cloud-based communications and collaboration solutions for small business and enterprise companies
draw.io - Online diagramming application
Dialpad - Switch is a cloud-based phone system built for Google Apps users.
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.
Aircall - Aircall is a call center software of a new generation designed for fast growing companies. Setup instantly and integrates to your CRMs
PlantUML - PlantUML is an open-source tool that uses simple textual descriptions to draw UML diagrams.