This is Inform 6.41, copyright (c) Graham Nelson 1993 - 2022, a compiler for interactive fiction (text adventure games).
Release notes, manuals, executables and more are available from https://ifarchive.org/indexes/if-archive/infocom/compilers/inform6/.
Back in the late 1980s, people began investigating the format of Infocom's text adventures. Infocom used a standard format that defined a virtual machine, which has come to be known as the Z-Machine, to allow them to be able to port their games to many different computers. This investigation lead to the creation of open source implementations of the Z-Machine, such as the InfoTaskForce interpreter, Zip, Frotz, and many others.
In 1993, Graham Nelson released the first version of Inform, which compiled a somewhat C-like language ("Inform") to the Z-Machine. In the years that followed this led to the creation of hundreds of free games by a community that had sprung up based around the Usenet group rec.arts.int-fiction.
The latest version of Inform is Inform 7, but Inform 6 still lives on, both as the code generator used by Inform 7, and as a language and compiler in its own right. Inform 6 is now considered stable and only has bugs fixed and minor, non-breaking features added, but development continues.
Using Inform 6
To use the compiler, you will need an executable. There are pre-built executables available, or you can compile the source yourself. There is no makefile as compilation does not really need one: all that is required is a C compiler and for it to be invoked with something like
cc -O2 -o inform *.c
Suitable defaults for various operating systems can be selected by defining the appropriate symbol, a list of which are near the top of the "header.h" file (under "Our host machine or OS for today is..."). For example, to compile for Windows, use
cc -DPC_WIN32 -O2 -o inform *.c
To write a work of interactive fiction with Inform 6, you will also need a version of the Inform 6 library. Stable versions of the library are available, and development of the library continues in a separate project.
More resources and documentation, including the Inform Designer's Manual, are available from the Inform 6 web site.