It depends on what you want to do as graphics and interaction since D&D requires a lot of stat calculations, but you can try RPG maker 3000:
https://www.rpg-maker-downloads.tnrstudios.com/
I thought RPG maker is illegal since it was translated to English and distributed free of charge even though it was a commercial product? Also may I reccommend RPG Toolkit. Its free even for commercial use, and it has a great community. Or you can try making a Role-playing Game using Multimedia Fusion. Its very difficult at best since the software isn't designed for Role-playing Games in particular, but it can be done and heres the proof.