TYPO3 is a free and open source web content management framework and content management system, which has been released under the GNU General Public License. It can run on several web servers, such as Apache or IIS and on top of many operating systems like Linux and Microsoft Windows.

The TYPO3 content management system makes it very easy for a web shop or web site user to manage the web shop or site without needing a technical background.

The TYPO3 content management system contains several features that will make the management of your web shop or site very easy. These features are:

Rich Text Editor (RTE): multiple RTEs with Microsoft Word-like icons, support for Win/IE, Mac/Safari and Mozilla Firefox on all platforms; WYSIWYG editors are highly configurable -- buttons and CSS styles can be added and removed;

Intuitive UI: the site is organized and displayed in the backend in a page-tree format that duplicates the structural layout of the site. File management functions are displayed in a directory-tree format that duplicates the directory structure of the installation. This makes finding pages and files easy for content editors;

Spell Checker: the spellchecker is built into the Rich Text Editor;

Configurable UI Levels: Customizable/Skinnable backend interface for editors (expert or newbie interfaces); Help icons are located beside most functions;

Undo / History: TYPO3 has unlimited history. You can undo any change you make on the site; 
 
Clipboard: copy and paste single or multiple pages and content; 
 
Frontend or Backend Editing: users can choose to edit in either the frontend (directly on the webpage) or the TYPO3 backend; 
 
Preview Content: hidden, time- or access restricted content can be previewed online before publishing;

Multiple Page Editing: any level of pages can be loaded into an editing form by specifying parameters such as name, date online/offline, etc. to be edited at the same time;

Minimal Training Required: editing content in TYPO3 is as easy as editing in Microsoft Word. Menu links are automatically generated as an editor adds pages and most content elements feature wizards for further ease-of-use;

Internal Shortcuts: repetitive operations and frequently used internal modules can be captured as a shortcut in a single click. Having a collection of shortcuts, users can jump around inside TYPO3 with little effort. Shortcuts can be grouped, named and even added to user groups by administrators; 
 
Live Search & Replace: an extension provides a way for editors to have access to a shorcut repository for commonly used phrases, names, text, HTML and code. If you update the shortcut, it updates all the instances of it on the site;

Wizards: content wizards exist for forms, tables and image manipulation;

Task Center: ability to create and manage projects, email project members, edit recent pages, view/manage inbox, insert notes onto webpages and create special actions for downloading CSVs of parts of the database or setting up backend users quickly; 
 
Internal Search Engine: editors can perform a search for a keyphrase within a section of the site. The results will return all the content elements with the phrase included. These can be edited at the same time. An extension performs a similar function, but allows the string to be replaced;

Creation: create (unlimited) pages, content elements, (mail) forms etc.

For a full overview, please check this link.