Les Paul Playable guitar seen in today's google.com doodle

They are using HTML5, javascript and Flash.  It can be done by HTML5 and javascript alone, but they use Flash because of some older browsers doesn't support HTML5.

If you go to view source, you should see this

<canvas width="474" height="175"></canvas>

They are using a <canvas>- Might be to draw the guitar. And then a javascript call google.doodle.go(); on the click.

http://www.pcworld.com/article/229878/les_paul_google_doodle_lets_you_strum_guitar_record_playback.html

http://www.geek.com/articles/geek-pick/google-doodle-is-a-working-les-paul-guitar-2011069/