Lucidchart is a web-based application to draw diagrams.

yEd is a free general-purpose diagramming program with a multi-document interface.

PlantUML is an open-source tool allowing users to create UML diagrams from a plain text language.

draw.io is free online diagram software for making flowcharts, process diagrams, etc

Creately is a collaborative diagramming and design software used by teams around the world to communicate more effectively.

ProcessOn is an easy-to-use, free and powerful online diagram designer which support to share and real-time collaboration.