When our website was down due to maintenance, we used to run JSTetris on the error page, so people would stay on the page, and they would get redirected to the web site as soon as the maintenance was over.
Some people even complained that they shouldn't be redirected automatically because they'd lost their progress :)
Games on the Commodore 64 started doing that in the early 80s. Loading from the cassette could take ages, so the devs would put in something like space invaders or missile command to entertain while the user waits for the main event.
