Sanitize $_REQUEST, $_POST and $_GET before the processing of TYPO3 in backend or frontend starts. Take a look into the documentation how to add your own rules or see which one exist.
Generic highly adjustable and extendable search engine framework, using Zend Lucene, Apache Solr or ElasticSearch. But support for other search engines can be provided easily.
Enhanced frontend user management for TYPO3. User registration, login and management in a single extension. (Most features still under development!) Requires PHP5!
This TYPO3 extension provides an API to communicate with socials networks. So it's possible for example to publish newly created news (or whatever you like) directly into social networks.