Drupal is a modular content management system, forum, blogging and community engine. It is database driven and can be used with MySQL, MariaDB, PostgreSQL, and SQLite. Its features include (but are not limited to) discussion forums, Web-based administration, theme support, a submission queue, content rating, content versioning, taxonomy support, user management with a fine-grained permission system based on user roles (groups), error logging, support for content syndication, locale support, and much more. It is considered to be an excellent platform for developers due to its clean code and extensibility, and it can also be used as a Web application framework.
Cerb is a fast and flexible Web-based platform for business collaboration and automation. It helps you remember anything about anyone, collaborate from anywhere, deftly reply to a flood of email, automate, stay informed, capture feedback, track time, flag opportunities, manage tasks, share expert knowledge, and otherwise execute efficiently.
phlyMail is a groupware, webmailer, and PIM. It offers unlimited nested groups, unlimited POP3/IMAP profiles, quotas, an integrated address book, a calendar with multiple reminders and event repetitions, a file manager with an integrated WebDAV server, the ability to send faxes, SMS support (which lets you send SMS, get reminded of events via SMS, and get email notification via SMS), a bookmark manager, themes, and multilingual support. It uses either sendmail or SMTP to send email, and can handle MIME and SSL connections. Support for IDN (Internationalized Domain Names) is included. Through its modular design, it's easy to add completely new features as modules, which can be plugged into the system.
WebsiteBaker is an easy, secure, flexible, and extensible content management system. Templates can be created within minutes and are powered by (X)HTML, CSS, and jQuery. Droplets provide a new and revolutionary way of inserting PHP code everywhere you want. Many extensions are available and can be installed and used with two clicks. A flexible API is also provided.