A number of Scrabble variants have been played by Scrabble expert players. One of the more popular ones, reputedly used by perennial champion, David Gibson, and his wife is to set aside a blank for each of the players (always a 2-player game) - and allow the player to use the blank, in combination with the 7 tiles on the rack, on each turn until the player actually chooses to play it. A bingo bonus of 50-points still requires that all the 7 tiles on the rack be used - so it can be scored without using that eighth (blank) tile. If the blank is used, a bingo bonus is scored only if all 7 rack tiles are also used.
One I dreamt up (literally, the idea came to me in a dream) recently, and have tried it out with Joe Edley (another perennial champion), involves making a "L" shaped play each turn - rather than a straight line play. All plays must be 3 letters or longer. Forming non-words in the process is permitted, provided at least one genuine word is included in the play. Scores are made only for the real words (non-words are worth nothing). If a player declares a score which includes points for a word that is not real, the play can be challenged off the board. A false challenge - finding that the word in doubt IS in the dictionary - costs the challenger a turn. Our trial game proved to be a lot of fun.