Hi! Thanks for stopping by and thanks for the compliments. The DM Helper was built to support 5e D&D, but 95% of the functionality is system and edition independent.
The character and monster stats and most things associated with them are fairly focused on 5e, though. It is in our roadmap to improve on this, to also support other editions of D&D, and other systems like Pathfinder, however we have so much to do that it may yet take a while.
As far as the play is concerned, i think that the tracker and the initiative system would work pretty interchangeably, and you can input custom damage. the five foot square is the same, so the movement is no problem- just input the proper movement number.
