ATCSMon has seemed like it would be a great railfanning tool since I heard about it. But for us Mac users it wasn't available. You could run an emulator or you could run Windows on an Intel based Mac. But I wasn't interested in that. Both would require a good chunk of disk space, possibly a seperate partition. And they'd require paying money to the Evil Empire.
Now there is an alternative...Wine. Wine Is Not an Emulator layers a Windows API (Application Programming Interface) on top of X11, a standard Unix graphical interface.
It doesn't provide all of Windows, it provides just enough to run a program in. This makes for a minimal impact in terms of disk space and memory. It also seriously limits the impact of Windows viri.
It would be nice if WINE used Aqua, Mac's native graphical interface instead of X11. There is a move afoot to do this but it's not ready yet as far as I know. Using Aqua would make the whole thing more Mac-Like and likely simplify using it.
While setting everything up to use ATCSMon on a Mac can bw an endeavor, so far it works quite well. At this point I have successfully monitored data served over the Internet and hooked it up to a modified scanner.
ATCSMon on a Mac Installation Procedure
CodeWeaver is another option. It costs $40 and functions the same as Wine. I have never used it so I don't know if it works with ATCSMon but it sems like it should. It should be a simpler install process.
One feature of ATCSMon I've discovered is that some engines broadcast ATCS data about themselves. So far the only interesting data I've found is simply the road number. But just getting the info that engines are in the area can be useful in some areas. In one stretch of the UP (ex SP) Donner Pass route ATCS gave me about three minutes warning of a train approaching. I've only observed this on UP engines. Not all but most UP engines were transmitting data.