I have used two interactive FORTRAN77 interpreters written in Fortran but a cursory search
did not produce any copies of them.
There are at least two scheme interpreters written in Fortran
DISCUS had/has a FORTRAN77-like interpreter
I thought there was a FORTRAN77-like interpreter in ROOT from CERN,
but if there was it appears to be gone.
Westinghouse had a shell program written in fortran that incorporated graphics, a functional language and extensive math functions and a set of operators for working on tables of numeric values and self-describing data files that has been in use for at least thirty years although I do not know if it is actively maintained.
If I get some time I might be able to track some of those down. I know the scheme interpreters are used in actively maintained programs but I have lost track of some of the others
The NCL scripting language for NCAR graphics had a huge amount of Fortran in it and I believe the original was all Fortran-based; but I think it migrated toward C; not sure but it had a huge amount of Fortran libraries available from NCL and is still available but no longer supported.