HexaLex: The best moves in Scrabble are the ones in which you cram a word in a just a few open squares, linking it up with the surrounding tiles to create several words at once. HexaLex, which is basically hexagonal Scrabble with all of the attendant gameplay tweaks such a setup requires, provides many such moments, and its recent update brought crucial online multiplayer support. Scrabble purists might object, but the rest will find it a welcome lexical alternative. $3
Also works with the iPad