I didn't add some of your logic in yet, but this should be a great starting point:

```javascript
Handlebars.registerHelper("platform_summary", function(platforms, options) {
    var end = ".";

    options.hash.sep = ", ";
    options.hash.conj = " and ";
    return Handlebars.helpers.concat(platforms, options) + end;
});
```

```html
{{#platform_summary platforms}}<a href="{{site_detail_url}}">{{name}}</a>{{/platform_summary}}
```