Apple Software
From Wiki
Apple users can almost certainly use the same tools that the Linux users are. You will need to install the Apple Developer's Kit (with Compilers) to build AVR GCC, following the Linux/UNIX instructions. You will also need a Serial USB Dongle to program your STK500. You could also try running Windows programming software in an emulator, such as QEMU.
Please also check out the OSX-AVR project at http://sourceforge.net/projects/osxavr/
