Greeble is not for everyone. Greeble 3.3 is geared towards experienced PHP developers, with the assumption that each individual developer will prefer to modify the behavior of the source to suit his or her individual needs. For the more casual user, there are many more suitable alternatives for the time being, a few of which are listed here.

Drupal is a powerful content management system, which lets users power many different types of websites without knowing any coding languages.
Drupal is a registered trademark of Dries Buytaert.

vBulletin: Greeble originally aimed to be a free replacement for vBulletin, implementing all of its features and then some. However, vBulletin is extremely powerful and Greeble can't yet approach its features list. The downside is that vBulletin is professional software; you have to buy a software license to use it.
vBulletin is a registered trademark of Jelsoft Enterprises Limited.

phpBB is the most widely used free alternative to vBulletin, and is nearly as powerful.
phpBB is (c) 2007 by phpBB Group.

PHPwnage is Greeble's sister project, a lightweight open-source content management system developed entirely by my good friend Kevin Lange.
PHPwnage is (c) 2009 by Kevin Lange