Thanks to the Library, you get a bare-bones environment in which your players can receive commands, move around, and interact with things. The Inform program that you write then builds on this foundation, fleshing it out with your own rooms, objects and people. As with the Inform compiler, there are versions of the Z-machine interpreter readily available for PCs, Macs and most other things besides. So, it reads a Z-code file created by the compiler, and then displays the game's descriptions and command prompts in a scrolling text window. The operation of the compiler can be controlled in certain respects, using mechanisms which are rather sparsely explained in the Designer's Manual .
More detail is available from the compiler's help, but people often forget to look there.
Version 5 Z-code. You can read about Glulx, and also download copies of the new compiler, Library and Glulxe interpreter, from Andrew Plotkin's comprehensive pages . Seeing how successful this was, Infocom came into being to address the home computer market. Eventually, Infocom went out of business. Activision is believed to possess the ZIL source for ZORK, Enchanter and all the other 30-some Infocom games, but has never made it available.