Excalidraw - Excalidraw is a whiteboard tool that lets you easily sketch diagrams that have a hand-drawn feel to them.
LetsDraw.It - Guess and Draw, Drawing Battle, Pictionary, Copy picture - online drawing games where you can compare your skill with others.
Drawasaurus - Drawasaurus is an online drawing & guessing game you can play with friends or strangers.
SketchParty TV - SketchParty TV is a high-tech drawing game that plays a bit like Pictionary.
iSketch - Isketch is a Free to play, Puzzle, Education, Word, Drawing and Multiplayer video game.
skribbl - Word guessing based on drawing.