iOS: If you want to play cards but don't have a deck, a free app called Card Table can do the trick. You need an iPhone or iPad touch and iPad to use it, but if you've got all that you just need people to play.
TRULY FREE iPad apps for teachers - we plan on keeping this list updated with favorites that are shared with us. AND...we plan on removing apps that end up not really being free. I hate when I download a free app and realize it only works a few times before you have to pay!