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

Grafio is a fun and capable diagraming app for iOS with plenty of features at a fraction of the cost of others.

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

ConceptDraw PRO is diagramming software used to create business graphics, including ConceptDraw Flowcharting Suite.