In the 1980s there was a puzzle magazine entitled "Scrabble Challenge". I don't think it lasted all that long but I thought it was rather good. There are several different varieties of postal Scrabble around, and this is a simple all-player version based on the old magazine game.
The game is played over a predetermined number of turns or until the tiles are exhausted (as will the players be by then!). Any number can play and people can join in at any time.
On the first turn there is an empty scrabble board and a rack of letters. Each player must use these letters to come up with the highest scoring word possible (as with a real game, the opening word must be placed so that one of its letters covers the centre square, which is treated as a double word score).
At the start of each round, the GM spends exactly 10 minutes coming up with the highest scoring word he can. The value of this word is published as the "target score"
Each player who equals or betters the "target score" gets a Victory Point. A VP is also awarded to the supplier(s) of the best score, even if it is less than the target score (if it is greater or equal, 2 VPs are scored in total). The points values of supplied words are recorded and Word Points totals are used as a tie-breaker in the event of equal VPs.
Words must be UK Official Scrabble Words which can be checked using Chambers Word Wizard or the newer Collins Word Finder which is now the official site.
After each turn, the highest scoring word stays on the board and new tiles are drawn at random from a real Scrabble set.
To help GMs, here is an old Word document containing an empty (colour) board.
This game has not been played in Variable Pig for 20 years but might be making a comeback soon...https://variablepig.org