3D Tetris:

(After long periods of exhaustive research, testing, and analysis:) Gnome 3D Tetris

• ANSI C code
• Apparently patched together from a core of some 3D tetris game written in French and miscellaneous other Gnome toolkit applications, provides a nice user interface.
• Added a custom C function (dump_world()) to give the internal state of the game to a pipe every time a brick falls. - No other modifications performed, meaning that the FEAtris interface still plays like 3D Tetris... (completing a layer will make it disappear, etc.)