KDE software is hosted on infrastructure managed by the KDE Sysadmins.
Find guidelines on: GIT LINK.
Some projects such as i18n (to localize the programs) or some websites still use SVN. The repository can be browsed on https://websvn.kde.org/. Some guidelines could be found in https://techbase.kde.org/Getting_Started/Sources/Subversion (TO BE MOVED).
The code is reviewed by the community before being pushed on a repository.