The internet is still relatively young, not even 50 years even if you count precursors, but the concept of hypertext is much older. One of the earliest written examples of hypertext is the Talmud, the 63-volume compendium of wisdom, law, and guidelines for life used by traditional Jews since its compilation over 1,500 years ago. Virtually every page of the text refers readers to other sources -- in fact, if you use some electronic versions of the Talmud, links to those references are included, though traditional Jews wouldn't use such a version on Shabbat or during chagim, good times for studying -- and if the text doesn't do it, the commentary will. A typical page of Talmud in contemporary volumes includes commentary from Rashi (11th century French rabbi known as the definitive commentator of virtually all Jewish texts to that time), Tosafot (medieval critical and explanatory commentaries), a series of cross-referencing tools, and sometimes a few other commentaries.
The Talmud was originally passed down orally; it wasn't redacted until about 1500 years ago, but even then it still had to be memorized -- it's not like there were enough copies for everyone to have their own. But even with the advent of the printing press, there has never been a widely recognized, accepted index.
The index has 6,600 topical entries and 27,000 subtopical entries that point students to the treatises and pages of text they are seeking. In these passages, sages analyze matters like whether one can remarry a former wife after she has been betrothed to another, or how one should handle a lost object found in a garbage heap. The index guides the student to significant laws about Sabbath and daily observance, as well as maxims, parables, commentaries and Talmudic personalities.
The index was compiled by an immigration lawyer, Daniel Retter (though it's been hechshered by some leading Talmudic scholars). When asked why he invested so much time and effort into this project, he said the following:
I’m a lawyer, and if I want to know the law, I look it up in an index.
Sounds reasonable enough to me. That's pretty much what we all do, regardless of our professions -- if we want to know the exact facts about something and don't necessarily trust our own memories for every last detail, we look them up. And it's helpful to have a handy reference to make it easier.
This is one of the things I've always loved about our traditions -- no matter how much we've studied, no matter how well we know our material, we still recognize that we can come up with better ways to learn. Even if it takes a few hundred years.
Also posted to The Progressive Zionist.