Get all models in backbone collection where attribute is NOT equal to some value

I don't know of something that's a direct opposite, but you can use a filter to the same effect.

var notMusketeers = friends.filter(function (friend) {
  return friend.job !== 'Musketeer';
});

If you're using filter directly on a Backbone collection, you must use it this way:

var notMusketeers = friends.filter(function(model){
    return model.get('job') !== 'Musketeer';
});

Then notMusketeers will be an array of Backbone model instances.

If friends is just an array of objects (standard collection), you could use the underscore filter this way:

var notMusketeers = _.filter(friends, function(obj){
    return obj.job !== 'Musketeer';
});

ES6

If ES6+ features are available to you, const, destructuring and arrow functions could make it a little less verbose:

const notMusketeers = friends.filter(({ job }) => job !== 'Musketeer');