For those who remember them, the gamebook was (and still is) the print world's answer to a computer role playing game.
These are typically novel-length books that rather than having a linean chapter after chapter read-through, instead give the reader a choice, granting active participation. Each chapter ends in a cliffhanger, and the reader is given the option of two or more different things they would do in this situation. Each choice instructs them to move to a specific page, and start reading the chapter following that point.
It is not at all unusual for a gamebook to have several hundred chapters, and most will not be reached on the first read-through.
To discourage linear reading, the chapters are often jumbled: For example, the first chapter is always in the right place, but may be followed by the 50th chapter, with the 17th directly after it. Thus, it is impossible to keep any sense of narrative flow from a linear read-through.
More advanced gamebooks use chance and scoring systems to determine progress. With a chance system, he main character might attempt to leap a ravine. Using a dice supplied with the book, the reader must roll to see if they make it, and turn to the chapter indicated by the number rolled.
With a scoring system, some chapters might result in the player's character being given new abilities, or spells. Perhaps they might find a certain amount of treasure. Later, if they have enough money, or a powerful enough spell (with the ability to use iot) they may choose different branches of the story than are otherwise available. The most advanced of this type, cross several books. A spell your character learns in book 1, might only first be usable when your character is strong enough, in book 3 for example.
No cRPG has been able to offer as many ending possibilities as a gamebook - most only have two (succeed, die horribly), so it is puzzling to note that the two types of adventure have grown up side by side. CRPGs have high artwork demands yes, and as usual, many things that are easy to do in prose, are very hard to do graphically, yet, it is still always surprising that multiple-endings in the computer based counterparts are far rarer, and usually a real marketing novelty.
In gamebooks, you often play through the same chapters with different choices; each just has differing preceding chapters, so its not as if the content creation argument holds that much weight. The gamebooks can get away with it, as different choices grant the character different abilities first.
Fundamentally, any virtual gameworld that can duplicate even a fraction of the fragmented storyline and radically different endings of a gamebook - 40 completely different endings is not unheard of - will do wonders for its replayability, and its believability.
Perhaps it should be made a rule of development, that every developer read at least one?