For software that does not support FCIDUMP format, what format is used and how can we get the software to interact with FCIDUMP integrals?

GAMESS(US) has this facility implemented, but this feature may not be available in the public release.

MRCC

MRCC stores 1- and 2-electron integrals in an ASCII file called fort.55 which is formatted very similarly to FCIDUMP.

The fort.55 file stores the integral values and integral indices in exactly the same way as in FCIDUMP, but has a different header. One has to delete the header of the FCIDUMP file and replace it with something like this (here my example is for the frozen-core carbon atom with an aug-cc-pVDZ basis set):

                    22                     4
                     1                     2                     3
                     5                     1                     2
                     3                     5                     1
                     4                     6                     7
                     1                     2                     3
                     5                     1                     1
                     4                     6                     7
                     1
 0
  0.43849259240468241305E+00   1   1   2   2
  0.43849259240468135834E+00   1   1   3   3
  0.48783372394503787817E+00   2   2   3   3
  0.51270165447111978874E-01   1   2   2   5

In the fort.55 header shown above, the 22 is the number of spatial orbitals, the 4 is the number of correlated electrons, and the 22 following numbers are the irreps for the spatial orbitals (in this case the carbon atom is being treated with $D_{2h}$ and you can use my Quantum Chemistry Cheat Sheet to convert between the numbering conventions of some of the most popular quantum chemistry codes (for example my cheat sheet tells you that the $B_{1u}$ irrep is 5 in MOLPRO but 6 in MRCC).

Once you have converted your FCIDUMP file into a fort.55 file, you now have to "trick" MRCC into reading it (because by default MRCC is not meant to be reading in other program's integrals except in the specific cases where an interface has been written to communicate with a program).

This can be done by using the keyword iface=cfour, which makes MRCC think that it's getting a fort.55 file printed from the CFOUR-MRCC interface, when really it came from an FCIDUMP!