Numble
Numble is a 1965 board game published by Selchow and Righter which is very similar to Scrabble. Instead of forming words, players form sequences adhering to certain arithmetic and numerical constraints.[1]
Each tile in Numble has a single digit, 0 through 9, except for two blanks. A "word" in Numble is a string of digits in sequence (in either direction), except that a zero is allowed at each end, with duplicate digits allowed (except for having more than one zero at either end), and where the sum of the digits is a multiple of 3. For example, 0,1,1,3,6,7,0 is a valid sequence, as is 7,6,3,1,1. Each tile is worth its digit's value in points.
A blank could be placed anywhere and, unlike in Scrabble, did not count as a particular digit, so the same blank tile could, for example, be between 3 and 4 in a horizontal sequence and between 8 and 9 in a vertical one.
Some other differences from Scrabble are: a rack is six tiles instead of seven; the center square is not a "double word square"; and, playing all six tiles in your rack at once scores a 10-point bonus instead of 50.