Frolg is a Z-machine assembler written by User:Zzo38. It is written in C, and is licensed under GNU GPL 3 or later version. Both Inform and Infocom names for opcodes are supported, and macros are also supported. All Z-machine versions from 1 to 9 are supported.
It is designed to be used with the Berzio compiler and for writing the codes yourself, although the author suggests also writing programs to convert text-adventure games from other systems into Z-machine, possibly going through Frolg or another assembler.