According to the post by Dries on his website:
Today, we are happy to announce that we'll start to provide free Acquia Hosting accounts to not for profit sites that promote Drupal adoption and usage. For example, DrupalCamp websites and local Drupal user group websites would qualify for free Acquia Hosting. The program starts in October or November, but you can sign-up now if you have a site that qualifies.
In exchange for free hosting, we require that the footer section of each page displays "Hosted by Acquia", and that an Acquia logo is displayed somewhere on your homepage.
If your site meets the above criterion, and you wish to enroll in Acquia’s Free Hosting program, you can sign up and we'll let you know when we are ready to host your site.