The Mac OS X equivalent is probably the revolving colored "beachball", or whatever Apple calls it. The nice thing about it though, is that unless in the Classic environment where the bomb freezes up the entire system, Mac OS X code is so compartmentalized,/sandboxed, that usually, only the app in use is affected, and can be forced quit, leaving the system as a whole, running. So that is one big improvement from OS 9 to OS X which I appreciate.

The fact that one does not need to set a memory allocation for each individual app is also nice.