In the time-wasting sense:
The Integer Basic games that came on cassette and had an Apple I heritage, ESPECIALLY
Apple Trek but to a lesser extent Breakout and Pong too
Beagle Bag, or Applesoft Basic and any Beagle Bros catalog, or just a Peeks and Pokes
chart.
Lemonade
Sabotage
None are killer apps
But all are excellent fun
Tim.