OSTree allows clients to atomically upgrade and switch between multiple versioned filesystem trees. It was designed from the start to complement package systems like RPM and dpkg.
It offers a middle ground between the extreme flexibility of package systems, and the singular OS vision of operating systems such as ChromeOS.
Being less flexible allows OSTree to (in some scenarios) be much faster and more reliable than packages, which is an important component of doing continuous integration and deployment. For example, this talk will discuss releasing Fedora 100 times a day or more, rather than just "nightly".