If you were planning a day of productive work, you may want to reschedule: the Internet Archive has created an online arcade which lets you run over 900 classic games right there, in your browser.
Not all of them work perfectly but there are just so many. Scrolling through the selection on offer will likely send pangs of nostalgia flying in all directions. Then you'll start playing them and forget about real life entirely. Sure, there are other ways to play arcade games online, but this resource just has so many in one place that you may as well forget about the rest. Golden Axe? Yep. Hang On? Of course. Commando? Hell yeah. (Those ones, as you may've guessed, were my childhood favourites.)