In school, most of us learn the significance of Gutenberg's invention of the moveable-type printing press. However, there's relatively little discussion of the development of other duplication technologies, such as hectograph, mimeograph, and spirit duplicator (ditto) technologies, made it possible to produce small print runs quickly and cheaply, without the investment of typesetting.
One can make a good case that short-run duplication technologies represented an innovation at least as significant as the printing press. In the mundane world, it enabled businesses to produce internal newsletters and circulars, churches to produce weekly bulletins, schools to produce worksheets and tests. Anyone of a certain age has recollections of the head-rush that would come from breathing in the vapors off a freshly-run ditto-coped worksheet or test.
In the fannish community, these technologies were really what made fanzines possible. Fans first started connecting with one another via the letter columns of the early pulp sf magazines. In those days, it was normal for the letcol editors to publish the full addresses of the people who wrote letters, so other readers could contact the commenters directly. It didn't take long for fannish communities to develop, and while some formed in-person clubs with like-minded individuals in their communities, others developed by-mail communities.
The earliest known fanzine is The Comet, a production of a group of 1930's science fiction fans. The fanzine scene quickly exploded as a community already fascinated with science and technology discovered that short-run duplication technologies were easy to implement, often with DIY tools. The hectograph in particular was astonishingly easy to set up, consisting of a tray the size of a sheet of paper, filled with a special gelatin. The master copy was made with special inks, then placed on the gelatin, which would absorb the inks. Copies were made by pressing blank sheets of paper to the inked gelatin, which would then transfer to the page.
Hectography had the advantage of being cheap and easy to set up. It also was the only duplication process that readily admitted the use of color. However, it had several downsides. Duplication was limited to 20-80 copies, depending on the quality of the original and the skill of the person using it. The gelatin bed was fragile, and a careless touch could ruin the image in it. Bleaching the gelatin for a new page required a significant amount of time, so multi-page zines needed serious planning. But it did make it possible for large numbers of fans to "pub their ish" on a reasonably regular basis.
Because of the very low limit on the number of copies one could make with a hectograph, larger-circulation fanzines moved to mimeograph and spirit duplication technologies. The terms "mimeo" and "ditto" were often used interchangeably, but they were two very distinct technologies that required different techniques to produce the master copies. However, both were reasonably inexpensive, especially for an amateur publisher who wanted to include artwork. Although neither mimeo stencils nor ditto masters could be used indefinitely, they could produce hundreds of copies, which was enough for the largest fanzines.
A spirit duplicator was generally less expensive than a mimeograph machine (which was why there were so many in schools), but it had one big disadvantage: the purple ink has a strong tendency to fade if exposed to light. This wasn't a big problem for school worksheets or church bulletins that were intended to be ephemeral. However, it's become a big problem for archivists trying to preserve the history of institutions -- or of fandom. All those dittoed fanzines are fading to illegibility, and with them, the articles and fanfic that tells the story of those early generations of fans.
By the 1970's, xerography had become common enough that most fanzine creators had access to a printshop that could duplicate typed masters quickly and cheaply, without the mess and finickiness of the earlier duplication technologies. By the 1990's, most fans had at least some access to computers, and fanzines were increasingly being produced with word processing and digital prepress software (PageMaker and the like). The twenty-first century has seen a movement of fanzines away from paper to Internet distribution, whether via e-mail or downloadable on websites.
However, while those early technologies have by and large been superseded (save by a few people who continue to use them for nostalgic or artistic reasons), this is by no means to denigrate them. Technologies such as the hectograph, mimeograph, and spirit duplicator helped develop a market that would make xerography such a success when it came along.