Play any type of Game at Y8.com. The biggest Game Collection to play free online. Flash, Unity 3D, Html5, Android, Java and Shockwave.
If the game freezes, just click inside it (games can get unresponsive if you click elsewhere on the page).
Try to do all the things during office hours but don't let your boss know! If the boss comes out, just click the computer to resume working. Don't get caught or you'll be screwed.