Epic Pen lets you write and draw over any software. It's a screen-marker and digital whiteboard tool for Windows.
Epic Pen is a small toolbar that sits on top of other windows, and you can easily select cursor, pen, eraser, pen size, undo, and clear screen. A screenshot function is available. It's simple to use and learn. The third screenshot below shows us writing over Google Chrome within minutes of starting.
As a freemium product, purchasing gives you a Line Tool, Text Tool, Whiteboard, Blackboard, and Vibrant Color pack.