Size, ability to have a single executable, requirement to display their copyright, and probably a few technical ones I can't remember anymore; I vaguely recall

Size, ability to have a single executable, requirement to display their copyright, and probably a few technical ones I can't remember anymore; I vaguely recall stuff about DOS4GW being more strict with certain CONFIG.SYS and HIMEM settings, but it was almost 20 years ago. :)