Constrained writing is an idea as old as writing itself. It has gained popularity since about 1960, when computers first started being used by some experimental writing groups to manipulate text.

Members of the French group Oulipo are the main devotees of this writing style. Raymond Queneau, a Frenchman, wrote a "book" called 100,000,000,000,000 Poems, which had a unique structure. The poems were each produced from a combination of 10 primary sonnets, from which verses were chosen at random. After this "book" was published, Oulipo was created in 1960.

Oulipo still has active members, including Jacques Roubaud, who has written three autobiographical novels which are read through "interpolations and bifurcations" of a tree structure with various added material. This is a real hypertext novel, and Roubaud has said that the fourth part of his memoirs will be published online, I assume for maximum hypertext-ability.

Many mathematicians and computer science types also play with constrained writing, as number theory and programming languages can provide many complicated constraints. There is also an extremely peculiar newsgroup called alt.adjective.noun.verb.verb.verb, in which all posts made are of the form dictated by the group's title. The group was inspired by the existence of several newsgroups of the same titular construction, such as alt.swedish.chef.bork.bork.bork. People will rewrite and post a famous speech/scene/soliloquy so that it fits the form of the group's title.

Search for "mike keith" and "constrained writing" on a good search engine to find the pages containing two modified versions of The Raven. One encodes some digits of pi (as mentioned above) and the other has each line fitting the form alt.noun.adjective.verb.verb.verb.