Enigma is a puzzle game involving falling blocks, exploding bombs, and pushing stuff around. It has elements of Boulderdash and elements of Sokoban, and anybody old enough to remember XOR on the Spectrum will see large elements of that in it.

The game rules were devised by somebody who wishes to remain anonymous. He has donated the levels to the public domain. The implementation was written from scratch by Simon Tatham (http://www.chiark.greenend.org.uk/~sgtatham/).