Best tools for reverse engineering dos programs?

[pp2]

You should use dosbox or qemu for debugging or reversing. The main reason - these programs can emulate _every_ instruction and both opensource, so you can modify them to accompany your research.

E.g. you can add some unique feature: breakpoint on register value (break, when ax=3), breakpoint on memory value, breakpoint on register access, etc. This helps reversing a lot.