Adobe is just one of many companies producing products for PostScript, but it does produce a lot of the best.
Adobe offers two resources for software developers.
The Developer's Association is Adobe's way of knowing who has a serious interest in technical information. Membership includes monthly technical newsletter, phone technical support, discounts on software and hardware. Membership is $195/year for each individual.
The PostScript Language Software Development Kits collect all Adobe's technical literature for a given platform into a single package. There are four versions, for the Mac, MS-DOS/Windows, NeXTStep, and X/Windows. Each SDK is $500 list, $250 for ADA members.
A selection of free technical documents is available from Adobe's file server and anonymous ftp archive (ftp.adobe.com). It includes specs (including the aforementioned EPS specification), some tech notes, sample programs, a large collection of AFM files and PPD files. For more information on the file server, send the one-word message ``help'' to ps-file-server@adobe.com. These documents are also available by mail, although they are not necessarily free; call the Developers Line and ask for the documents catalog.
The contents of both ps-file-server and the ftp archive are nominally the same, although they are currently maintained on two separate machines.