The Scrabble app for iPad used to do that. There was a separate 'Tile Rack' app for iPhone. The iPad app for Scrabble was paid ($9.99 IIRC), but only one player had to buy it. The companion tile rack app was free. For some reason, EA seems to have removed that functionality:

https://boardgamegeek.com/thread/838860/scrabble-tile-rack-a...

https://twitter.com/askeasupport/status/237941190538977280