DrawPile - Drawpile is a drawing program that lets you share the canvas with other users in real time.
Drawasaurus - Drawasaurus is an online drawing & guessing game you can play with friends or strangers.
PaintTool SAI - Learn to draw in different ways.
skribbl - Word guessing based on drawing.
Excalidraw - Excalidraw is a whiteboard tool that lets you easily sketch diagrams that have a hand-drawn feel to them.
gartic.io - Draw, guess, and win!