An extension is a piece of software that extends or alters the functionality of TYPO3. Extensions let TYPO3 perform almost any function you could imagine.
Extensions can be downloaded from the extension repository (TER) on typo3.org and loaded into a TYPO3 website through the extension manager. Besides the Static Info Tables extension and the Templavoila extension, TYPO3Buddy has some other extensions installed.
- RealURL (realurl) - speaking paths for TYPO3, to make sure the website has SEO friendly URLs
- Custom page title (re_pagetitle) - creates a custom html title and includes page titles from the rootline (like a breadcrumb menu)
- JB GD Resize (jb_gd_resize) - to make resizing of images possible without ImageMagick
- Extension kickstarter (kickstarter) - to make new extensions
Installed system extensions:
- RSA authentication for TYPO3 (rsaauth)
- Salted user password hashes (saltedpasswords) - both to make sure the BE user passwords are not stored as easy-to-crack MD5 hashes in the database
If you're developing extensions, you can find valuable info about extension variables here.