Kicker
A simple OS X CLI tool which uses FSEvents to run a given shell command.

Usage
Give it paths to files or directories and a shell command to execute when any changes occur.
Usage: kicker [options] -e [command] [paths to watch]
-e, --execute [COMMAND] The command to execute.
--[no-]growl Whether or not to use Growl. Default is to use growl.
--growl-command [COMMAND] The command to execute when the Growl succeeded message is clicked.
Examples
Show all files whenever a change occurs in the current work directory:
$ kicker -e "ls -l" .
Run a Rake task whenever a given file is changed:
$ kicker -e "rake guides" guides/source/nested_model_forms.textile
Run a Run task whenever a given file is changed and specify a command to be executed if the user clicks a ‘succeeded’ Growl message:
$ kicker -e "rake guides" --growl-command "open -a Safari guides/output/nested_model_forms.html" guides/source/nested_model_forms.textile
And for fun, ghetto-autotest:
$ kicker -e "ruby test/test_case.rb" test/test_case.rb lib/file.rb
Installation
$ sudo gem install alloy-kicker -s http://gems.github.com