skribbl - Word guessing based on drawing.

Aggie.io - Draw a picture together with your friends in real-time over the internet in your browser.

gartic.io - Draw, guess, and win!

Pictar.io - Pictar.io is a Drawing and Multiplayer Puzzle video game available to play on the Browser.

Drawasaurus - Drawasaurus is an online drawing & guessing game you can play with friends or strangers.

Sketchful.io - Pictionary type game where each round a different player draws something that the other players have to guess the word for.