jquery.myplugin.coffee

$ = jQuery
$.fn.extend
  myplugin: (options) ->
    self = $.fn.myplugin
    opts = $.extend {}, self.default_options, options
    $(this).each (i, el) ->
      self.init el, opts
      self.log el if opts.log

$.extend $.fn.myplugin,
  default_options:
    color: 'red'
    log: true
  
  init: (el, opts) ->
    this.color el, opts
  
  color: (el, opts) ->
    $(el).css('color', opts.color)
  
  log: (msg) ->
    console.log msg

jquery.myplugin.js

(function() {
  var $;
  $ = jQuery;
  $.fn.extend({
    myplugin: function(options) {
      var opts, self;
      self = $.fn.myplugin;
      opts = $.extend({}, self.default_options, options);
      return $(this).each(function(i, el) {
        self.init(el, opts);
        if (opts.log) {
          return self.log(el);
        }
      });
    }
  });
  $.extend($.fn.myplugin, {
    default_options: {
      color: 'red',
      log: true
    },
    init: function(el, opts) {
      return this.color(el, opts);
    },
    color: function(el, opts) {
      return $(el).css('color', opts.color);
    },
    log: function(msg) {
      return console.log(msg);
    }
  });
}).call(this);

main.coffee

$ = jQuery
$ ->
  $('#world').myplugin();

main.js

(function() {
  var $;
  $ = jQuery;
  $(function() {
    return $('#world').myplugin();
  });
}).call(this);

Really should be setting $ explicitly on top. See: https://gist.github.com/912762

This is similar to the pattern you see in jQuery often:

(function($) {

  $.fn.plugin = function(){}

})(jQuery);

True, I did see a few things about that, but at the same time, my example worked in a little test html file of mine without it, so I decided to leave it out.