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
Nanonets - Worlds best image recognition, object detection and OCR APIs. NanoNets’ platform makes it straightforward and fast to create highly accurate Deep Learning models.
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.
Base64.ai - Extract text, data, photos and more from all types of docs
Dia - Dia is a GTK+ based diagram creation program for GNU/Linux, MacOS X, Unix, and Windows, and is released under the GPL license.
Unfreeze - Less typing, more coding