Versions are distributed with the R4, R5, and R6 releases. An earlier version
is distributed with the X11R3 release; some third-party toolkits redistribute
versions of imake along with their own implementations of the template and
configuration files. There are no real standards for such configuration
files, although most *current* contributed software expects the templates
distributed with X11R5 or X11R6.

ftp.x.org contains the R5 distribution unpacked, so you can pick up imake
without picking up the entire distribution.

A stand-alone version of Imake, but one stemming from X11R5, is in
ftp.germany.eu.net:pub/X11/misc/imake/imake-pure.tar.Z (192.76.144.75).

A stand-alone version of Imake, but one stemming from X11R5, is in
ftp.primate.wisc.edu:pub/imake-book/imake.tar.Z.