The Oregon Trail
putman10.github.io
putman10.github.io
Events also occur a lot more often such as thieves stealing your supply. You were also allowed to trade in case you lost your oxen which determines how far of a distance you can go each day. The total distance was also longer than just 500 miles.
But seriously, I played this on an apple 2 emulator a couple of years back, and it seems like the logic under the hood is a bit off. I wonder if the original source code is still available.