Since TYPO3 Sept 2014 twbs/Bootstrap is included in TYPO3 CMS backend.
Also the Bootstrap CSS documentation is included in EXT: styleguide.
Since TYPO3 version 6.2 Normalize.css is included in the TYOP3 CMS core.
Normalize.css is a project by Nicolas Gallagher, co-created by Jonathan Neal.
Source code available on GitHub: necolas/normalize.css. Thank you!
Clearfix is included since TYPO3 6.2. Thank you!