Wordloom saves today's puzzles on your iPhone ahead of time, so all five games play on a plane, underground or with no signal. Your results are kept on the device and post to your league automatically once a connection returns. If the app has never reached the server and has nothing saved, it builds the day's puzzles on your device.
It labels that day as an offline day that won't post to a league instead of showing an error screen. Practice rounds, the unscored games you can play after your daily five, are also generated on the device. You don't need an account to start either. Open the app and play, and sign in with Apple only when you want to join a league.
Download on the App Store