Libre office draw is wonderful, it can edit pdf docs at ease. It’s crazly powerful compared to paint 3d
draw.io - Online diagramming application
Eagle.io - Cloud-based environmental IoT platform
yEd - yEd is a free desktop application to quickly create, import, edit, and automatically arrange diagrams. It runs on Windows, Mac OS X, and Unix/Linux.
Perillon - Perillon is an EHS software that helps companies to achieve compliance with the relevant government rules and regulations.
PlantUML - PlantUML is an open-source tool that uses simple textual descriptions to draw UML diagrams.
Effective Software - Health & safety compliance management system | Health and safety software