X-CTU runs on a windows vm under Mac OS X (I used VMware Fusion and a windows XP).
The Xbee devices I am familiar with (a very short list) can be configured via a standard terminal application by putting it into a configuration mode (send +++ is the default), then configure with AT commands. This can be done with any terminal application on any operating system. you could probably even use the Arduino serial monitor.
I doubt you can do things like flash new firmware onto the xbee, but for changing addresses, baud rates, etc, it works just fine. Just read the manual to find the appropriate AT commands.
-j