TYPO3 is an open source enterprise Content Management System (CMS) used for websites, intranets, and online applications, from small to enterprise level companies. Other than having responsive design multi-platform capabilities, some great features of TYPO3 are: 

Security is a top priority: their support is great and their team is constantly working on looking for and disabling any security threats. 

Visual Content Editing: like many other CMS, TYPO3 also offers a Drag&Drop visual editor for editing content and images from various sources on your website.
Flexible Design and Presentation: allowing for maximum flexibility your website can either have a uniform and strict corporate design or a creative and standardized design for individual pages.  
Multi-platform Capabilities: you can manage several independent websites in a single system, with the option of sharing the content created across all of them. Protected Areas and Multilingualism: TYPO3 can also be used to create protected areas that can only be accessed by certain employees, customers or partners, with a sophisticated system for the administration of users and user groups, with which even complex and hierarchically structured concepts are possible. Unlike most other CMS, TYPO3 supports multilingualism at all levels, its administration interface has been translated into more than 30 languages, and you can also create your own multilingual content on your website. You can either offer individual areas of your website or the entire website in different languages.
Seo Tools In Typo3: With TYPO3, and its multitude of mechanisms for on-page search engine optimisation, you can achieve better search engine rankings thanks to fast loading times, mobile website display and optimized code structure.