Kaboom was a Bomberman clone that never saw the light of day, one of the infamous Games that weren't.
It got to a fairly developed Alpha stage before Wayne was tempted off to join the Reflections team of Psygnosis. Disk images of the alpha are preserved here.
A comprehensive history of Kaboom and its perpetual near-release status, including information from people involved in the sound and graphics for the game, can be found in SAM Revival issue 17.