Collabtive aims to become an alternative to tools like Active Collab or Basecamp. Features include management of projects, todo lists, tasks, milestones, and files, an easy to use interface, multi-language support, an AJAX-based instant messenger, and an AJAX-based online list.
MyOrgBook is an open-source project licensed under the GNU GPL. It is also an online organizer programmed with PHP and MySql. Some features include multi-user login, lost password emailer, contacts, todo list manager/scheduler, calendar, profile changer. MyOrgBook allows you to edit everything.
myphpim is a Multi-User, Personal Information Manager, including email client, addressbook, notes, todo and calendar, written in PHP.
Turba is a set of PHP scripts that implement a contacts directory and management interface. Turba also provides an API for external applications to interface with addressbooks, providing adding and searching features that you can hook right into other applications.
Web Organizer is a high-end GroupWeb providing Calendar, personal and shared Addressbook, Shared folders system.
Webdistro is a multi-user software suite written in PHP and providing a Web-based UI. It includes a calendar, todo-list, addressbook, and email.
worldpilot is a free, open-source, Web-based, multiuser organizer and messenger.