Yes. Our servers support having more than one alternate name for your site (such as www.example.com and another.example.org). If you visit the Sites panel and then select your site name in the "Short Name" list, you will see the Site Information page, where you can add and remove aliases at any time.
You may also add NearlyFreeSpeech.NET DNS to an alias at any time by visiting the Domains panel and choosing "Add" under the "DNS" column for the relevant alias (domain).