Alfresco is the first open source enterprise-scale document management system that includes a modern content repository, an out-of-the-box portal framework for managing and using content designed to work with standard portals, and a groundbreaking Common Internet File System (CIFS) interface that provides Microsoft Windows file system compatibility. Alfresco takes the lessons of building document management systems for the last 15 years and applied them to build an open source content management system that is easier to use, more scalable and more adaptable.

Plone is easy to use. The Plone Team includes usability experts who have made Plone easy and attractive for content managers to add, update, and maintain content.
Plone is easy to install. You can install Plone with a click-and-run installer, and have a content management system running on your computer in just a few minutes.
Plone is international. The Plone interface has been translated into over 30 languages, and tools exist for managing multilingual content.

Drupal is an open-source platform and content management system for building dynamic web sites offering a broad range of features and services including user administration, publishing workflow, discussion capabilities, news aggregation, metadata functionalities using controlled vocabularies and XML publishing for content sharing purposes. Equipped with a powerful blend of features and configurability, Drupal can support a diverse range of web projects ranging from personal weblogs to large community-driven sites.