Because TYPO3 development using piBase became less and less transparent, and lost a clear programming structure, TYPO3 developers began looking for a new and better solution for the future of the system. After looking at many frameworks in detail, the developers couldn't find one without any disadvantages, so the decision was made to develop a completely new framework: TYPO3 FLOW.
TYPO3 FLOW is the basis of the newest versions of TYPO3, formerly code-named “TYPO3 NEOS” (also “Phoenix”). Because of the completely new logic behind the new framework, TYPO3 FLOW was developed and is maintained within the system extensions, and not as a part of the former TYPO3 4.x core. Maintaining the technology within the system extension environment enables developers to begin working with it as soon as possible. This allowed the rapid development of system extensions extbase and fluid, which have enabled the integration of Extbase extensions to the CMS since TYPO3 4.3.