Package command line tools into an automator script or app?
All macs have several shells available (GNU bash 3.2.48 ships with the latest Snow Leopard) including zsh, sh, bash, csh and ksh. You can safely embed one or more shell scripts without fear that other macs won't have the tools to run your program.

The simplest thing to do would be to just embed a functioning shell script in an AppleScript or Automator workflow. Both handle piping arguments or file paths to stdin/stdout so you can interact with the script if desired.

The site Mac OS X Automation has some great tutorials to get you started if this makes sense to solve your issue.

Also, if you are looking for a tool to package your bash script and an automator/applescript document in one nice unit - the package maker application is available for free as part of the iPhone Configuration utility. It's more work, but will make any mac user more comfortable installing your tool.

For an open source option that is amazing - try Platypus - http://sveinbjorn.org/platypus/