All MFORTH development can be done on the M100 using the built in TEXT editor. MFORTH can read .DO files from memory and supports multiple levels of source file inclusion. Interactive development is supported by way of the standard Forth text interpreter.
The best way to use MFORTH is with REX on the real Model 100 hardware. REX is a plug and play flash memory upgrade for your laptop that allows you to easily use a variety of Option ROM images on your M100.
You can also use MFORTH in Virtual-T, which is especially helpful when working on the MFORTH kernel itself. I primarily develop MFORTH in Virtual-T and then move MFORTH builds to my Model 100/102 laptops for testing and application development.