skribbl - Word guessing based on drawing.
miniPaint - Online graphics editing tool use HTML5 technologies like Canvas, Offline support, Drag and Drop.
LetsDraw.It - Guess and Draw, Drawing Battle, Pictionary, Copy picture - online drawing games where you can compare your skill with others.
RealWorld Paint - RealWorld Paint is an free portable image/photo/animation editor.
gartic.io - Draw, guess, and win!
Paint XP for Windows 7 - Standalone old MS Paint program that allows you to get your old XP Paint interface in Windows 7.