Lucid Chart is a free tool for visual communication.
"Lucidchart helps students and educators make diagrams that are useful in the classroom,
like flowcharts, mind maps, UML diagrams, and venn diagrams"
Links and tutorials:
Comprehensive Guide Resources Page - https://www.lucidchart.com/pages/resources
Lucidchart Educational Homepage - https://www.lucidchart.com/pages/usecase/education
Thanks to Dr. Alvina Pauline Santiago for the information on Lucid Chart.