unecm trouble mac os x 10.6.8
The cmdpack you downloaded are command line tools. If you have a recent mac, you should have downloaded the Mac OS X (64-bit, x86_64) version.

To use these tools, you'll need to venture into the UNIX command line. This is analogous to the command prompt of Windows, and can be accessed using the Terminal application in /Applications/Utilities.

Once you've downloaded the cmdpack.gz file, uncompress it to a directory by double-clicking it. For ease of explanation, then drop the .ecm file you want to work with into that directory. Open Terminal (either find it in Utilities or Spotlight search for it) and then navigate to the cmdpack directory (the easiest way to do this is to type cd followed by a space, and then drag the directory to your terminal window--the path of the folder will be inserted--then hit return).

When you're in the appropriate working directory, you can type ls to list its contents. The executable you want to run is most likely unecm. The easiest way to run an executable in your current working directory is by prefixing it with ./. If you type ./unecm, the command will run and show you usage information. If you already dropped your .ecm file into this directory, unencoding it should be as simple as ./unecm myecmfile.ecm

To recap:


Download the Mac OS X (64-bit, x86_64) command-line pack and uncompress/ungzip it.
Open Terminal and navigate to the uncompressed directory (for me this command was cd /Users/nreilingh/Downloads/cmdpack-1.02-macosx-x86_64)
Run unecm as necessary with ./unecm after cding to the ungzipped directory.