Beyond the Tesseract

Early (1983) TRS-80 BASIC text adventure game, the middle in a forgotten trilogy (sandwiched between "Project Triad" and "Codename Intrepid"), remembered for its no-holds-barred approach to math and logic concepts informing game settings and puzzles: in one section, sparking a genre cliche, one has to play a text adventure game inside the text adventure game; in another, one falls asleep and in a dream constructs a proof utilising physical representations of various components of symbolic logic; additional game areas are accessed by pushing and popping the stack, objects extruded from 2 to 3 dimensions by _y_ing them.

The supporting documentation understates when it claims the scenario for the adventure is meant to be vague -- searching for a 12-word code phrase (unlocked in chunks upon completion of certain puzzles) is just an excuse for sending an unwary player through an alien and abstract setting two words at a time (using VERB NOUN gameplay with a vocabulary of about 200).

Later (1988) versions of this game were ported in C to Solaris, Atari ST and MS-DOS environments; more recently, in December 2003, Andrew Plotkin ported it to the interactive fiction standard of machine-independent Z-code.