To program AVRs in Mac OS X, you will need the free avr-gcc compiler, avr-libc, AVRDUDE, and other associated tools.
Download the CrossPack for AVR Development, which is packaged as a .dmg file. Open the .dmg file, and double-click on CrossPack-AVR.pkg. This package will create a directory called
CrossPack-AVR-<package-date> on your hard drive (probably under
/usr/local/) and add its
bin directory to the PATH environment variable.