TYPO3 v7 has reached its end-of-life November 30th, 2018 and is not maintained by the community anymore. Looking for a stable version? Use the version switch on the top left.
There is no further ELTS support. It is recommended that you upgrade your project and use a supported version of TYPO3.
Since TYPO3 4.4, the TYPO3 backend relies primarily on ExtJS. As of TYPO3 6.0, jQuery was introduced in the new Extension Manager and is the library of choice for the future. Since TYPO3 7.4, Prototype and Scriptaculous are not packed with the Core anymore. If you need them for your projects, you need to take care of shipping them yourself, preferable by usage of requireJs.