Libre office draw is wonderful, it can edit pdf docs at ease. It’s crazly powerful compared to paint 3d
YouiDraw - Draw and Design Vector Graphics, Logo, Text, icon in the Cloud.
draw.io - Online diagramming application
Aphalina Designer - Download this app from Microsoft Store for Windows 10, Windows 10 Team (Surface Hub). See screenshots, read the latest customer reviews, and compare ratings for Aphalina Designer.
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.
DrawBerry - All the features of other vector editing applications such as Adobe Illustrator or Inkscape, in a...
PlantUML - PlantUML is an open-source tool that uses simple textual descriptions to draw UML diagrams.