FORTRAN IV/66 ... a very old language for maths
As a foreword: I am offering the following compiler just for educational, non profit purpose. If any of the former copyright holder send me a mail that this is unwanted, I will immediately delete the concerned file.
Here are the CP/M Fortran compiler as complete packages:
Microsoft FORTRAN80 3.4 ...can be d/l'd from retroarchive.org
(please note meanwhile there is also a F80 version 3.44 available)
Nevada FORTRAN 3.0 ...can be d/l'd from retroarchive.org also,
a manual exists also.
SuperSoft SSS/FORTRAN 3.2 ... locally mirrored
Not really a full set of Fortran, but surprisingly running on a C64  Abacus Fortran64, see here for more info.
A book about FORTRAN IV for use with FORTRAN80 can be found here (attention, a PDF with a size of 7 MBytes !).
A manual for above mentioned Fortran80 3.4 can be found at bitsavers.org here.
Nevada Fortran Manual (C64 version, but for CP/M) exists here.
More FORTRAN stuff, but not FORTRAN IV/66 related:
A book about FORTRAN 77 written by Clive G. Page can be found at the pages of the University of Orleans, exactly here, even in PDF available here.
Compiles also Fortran (77) code: Open Watcom is available in source code and may be somebody is implementing a Z80 code generation ...
A MSDOS F77 Compiler (binaries only) named "BC Fortran" can be found at simtel's FTP here.
Gnu Fortran 77 (g77) 3.46 (this is NOT the newest one but supports older Fortran dialects) is located here (linux), manual can be found online. There is a shorthand option 'f66' which let compile Fortran 66 code easily (except computed goto).
A Fortran 95 Compiler (for Windows and Linux) can be found at g95.org.
Also, a modern F95 compiler (free for personal use) can be found at Silverfrost's page.
Silverfrost offers also an older F77 compiler there.
If you have to convert old Fortran IV/77 code, take a look here.
