draw.io - Online diagramming application
D3.js - D3.js is a JavaScript library for manipulating documents based on data. D3 helps you bring data to life using HTML, SVG, and CSS.
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.
Chart.js - Easy, object oriented client side graphs for designers and developers.
PlantUML - PlantUML is an open-source tool that uses simple textual descriptions to draw UML diagrams.
Google Charts - Interactive charts for browsers and mobile devices.