Carbon Visualiser - See your CO2 in burgers, basketballs, pufferfish and more
draw.io - Online diagramming application
Wren - Offset your carbon footprint by saving rainforests
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.
Website Carbon Calculator - Find out the how much CO2 your website emits
PlantUML - PlantUML is an open-source tool that uses simple textual descriptions to draw UML diagrams.