A Columns-like game. Line similar jewels together to clear them from the board.
The original shareware release required a 640x480 display. The commercial version added compatibility with 512x384 and monochrome screens, as well as a new suite of bonus jewels.
I found that if you set the monitor in classic control panels to 256, start Jewelbox, pause, then go back and reset to millions, it still plays fine and the OS X side doesn't freak.