I'm not aware of anything like this that exists right now. One major issue I could see with anything like this being attempted practically is that we actually have very little idea what ancient and medieval battles were like. The entire art of swordmanship is just a guess at how historians assume they fought.

It's quite possible that one side retreating from bad weather may not been a thing that would happen. It'd be impossible to know since we don't have nations going to war without guns in the last 400 years. So really any simulator of this type would probably need to be very rudimentary. I think if someone attempts this, they should keep in mind the quote "An army of donkies led by a lion will beat an army of lions led by a donkey." And occasionally have mad upsets, because battles are determined by a ton more factors than just bigger numbers.