It's the one that Norma provides on their site. All you need is muzzle velocity, ballistics coefficient, and wind speed and direction and site line height. You can adjust the zero distance to whatever you want. And once you set the variables you can figure out the trajectory and wind deflection at whatever distance you to know it at.
It took a minute to figure it out. But I think it's one of the better ones. The only real flaw that I found is that you can't save and compare bullets. But whatever, it's free and easy to use.
Just click on the ballistic tab. I'm guessing you'll want the US version. But there is also a metric version as well.