Ever wanted to quickly throw together an architectural diagram, a UML diagram or any diagram for that matter? Not everyone has access to Visio or an advanced drawing tool.
LucidChart is the current option of choice for most developers/architects looking to quickly draw a technical diagram. From wikipedia:
Lucidchart is a web-based diagramming software which allows users to collaborate and work together in real time to create flowcharts, organisational charts, website wireframes, UML designs, mind maps…
Another option is draw.io :
draw.io offers a clean , powerful UI to draw your diagram (online) and then export it as a .png image.