skribbl - Word guessing based on drawing.
Limnu - Sketch, share and collaborate with your team
LetsDraw.It - Guess and Draw, Drawing Battle, Pictionary, Copy picture - online drawing games where you can compare your skill with others.
Draw.Chat - Anonymous real-time whiteboard with text and video chat.
gartic.io - Draw, guess, and win!
Sketchboard.io - Visual Remote Teamwork. Solve problems and create ideas on endless whiteboard with your teammates by sketching.