I know NOTHING about FORTH but I just want something simple to mess around with.
I found a simple FORTH buried in a ZIP file on the Z80 info site at ...
http://www.z80.info/zip/z80asm.zip
I have no idea of it's origin but from snooping around it seems to be fig-forth-79 or based on that.
https://archive.org/details/FigFORTHGlossary
I combined it with Grant Searles initialisation and referenced the routines for the TXA and RXA where necessary.
Built with ... TASM -80 -b -c -dROM FORTH.Z80 FORTHROM.bin FORTHROM.lst ... For ROM binary
or
Built with ... TASM -80 -g0 FORTH.Z80 FORTHRAM.hex FORTHRAM.lst ... For RAM Hex file to run from Monitor
After some messing around and realising that I need to AND 7F to knock off the top bit of the characters as it uses this as an end of word marker.