In 2006, TYPO3 4.0 introduced Workspaces. The feature lets you have multiple versions of any kind of content, not publicly visible, but editable and previewable for editors within TYPO3. The content can be published to the so-called “Live” workspace, the actual website. You don’t need a second TYPO3 installation, the “workspaces” extension shipped with TYPO3 is enough.
This is a companion discussion topic for the original entry at https://typo3.org/article/workspaces-one-of-typo3s-most-underused-features