A free (libre), open-source (GNU GPL), content management platform designed for group collaboration. Open Atrium is based on Drupal (running on Apache, with a MySQL database).
With KeepNote, you can store your class notes, TODO lists, research notes, journal entries, paper outlines, etc in a simple notebook hierarchy with rich-text formatting, images, and more. Using full-text search, you can retrieve any note for later reference.