cc65 runs perfectly fine under various versions of OS X. While at the moment there are no up to date binary installation packages distributed, one can quite easily build his own binaries from sources provided as either stable versions in form of “tarballs” or check out the bleeding edge from snapshot directory or subversion repository.
Please note that in order to build cc65 from sources one requires a working UNIX development environment (especially GCC compiler), which is not a part of the default system installation. The requirements are then:
If you have downloaded the source “tarball”, extract the files from the archive to a directory of your choice. Since cc65 is very cleanly written - no additional configuration processes are needed. Once the necessary prerequisites are in place, start your terminal and cd to the directory where you have either extracted or checked out the cc65 sources. Simple command:
$ make -f make/gcc.mak
given from the directory you just cd'ed to, should be enough to build binaries, libraries, and documentation (the last only if the optional linuxdoc tools are installed)4)
Once the build process is finished without errors, the next step is to install the files in their default locations:
$ sudo make -f make/gcc.mak install
installs all the required files in their default location of /usr/local/5)
Building from source works 100% - tested
Building from source works 100% - tested
Building from source works 100% - tested
Building from source should work fine - untested
Building from source should work fine - untested
Building from source should work fine - tested, please consider switching to 10.4, which is (IMHO) the first mature OS X version
Building from source works 100% - tested, but while 10.2 was probably the first usable OS X version, you shouldn't really be running it anymore these days
Those were not really usable (IMHO) - I don't believe you might still be running it…