[Update 2016] Drupalgardens announced to its client that the service closes. Among all possible reasons for this, I retain the migration issue: migrating all those websites from Drupal 7 to Drupal 8 would be quite a challenge and is not the remit of such a Software as a service. The positive aspect is that each website is easy to archive / export and install on another hosting, Drupal 7 being still there for a while.
Drupal is a now famous open source content management. Easy to install, Drupal offers all the necessary functionalities (with a very strong taxonomy system), but also a lot of extensions through third party modules.
Recently, the latest barrier to offer Drupal to the masses has disappeared: Drupalgardens allows people without hosting to create a Drupal site for free, in a couple of seconds.
The free version includes a good set of modules, like forum, web form (100 limited to responses per form) and books. 5Gb of space is fair, but 5 users is limited (especially if you plan a forum).
But still, it is a good way to quickly start a site: if you wish to extend it, you may of course buy a plan; but you can also export the code and database to host your site where you want (hosting at 1 Euro / month is easy to find).
At work, we needed to build an event mini site with presentation of the event, and subscription form. Without previous knowledge of Drupal 7 (but being experienced with Drupal 6), it took us just a few minutes to set it up.
Open Source software really created a shift on how we use software. Freemium is everywhere, but being able to get your content back is really added value, keeping you free to choose the option that best suits your needs... or resources