challenges.hbs

<dl class="sub-nav">
  <dt>Filter:</dt>

  {{#link-to 'challenges' (query-params complete=false) tagName='dd'}}
    <a {{bind-attr href="view.href"}}>All</a>
  {{/link-to}}

  {{#link-to 'challenges' (query-params complete=true) tagName='dd'}}
    <a {{bind-attr href="view.href"}}>Complete</a>
  {{/link-to}}

  {{! How to get this one work, ie actually pass `false` to filter}}
  {{#link-to 'challenges' (query-params complete=false) tagName='dd'}}
    <a {{bind-attr href="view.href"}}>Incomplete</a>
  {{/link-to}}
</dl>

<ul>
  {{#each filteredChallenges}}
    <li>{{name}} / {{isComplete}}</li>
  {{/each}}
</ul>

challenges_controller.js

export default Ember.ArrayController.extend({
  queryParams: ['complete'],
  complete: null,

  filteredChallenges: function() {
    var complete = this.get('complete');
    var challenges = this.get('model');

    if (complete) {
      return challenges.filterProperty('isComplete', true);
    } else {
      return challenges;
    }
  }.property('complete', 'model')
});