Nightly builds allow the earliest preview of new features, bug fixes and integration of community contributions.
The nightly build of Alfresco Community Edition is available by downloading the development image from DockerHub.
Alfresco has a large set of automated tests and various builds run continuously when updates to the source code are made. Should a build pass all tests then it will be published to DockerHub. So a nightly build may from time to time be considerably older than 'last night'.
Nightly builds are unlikely to be suitable for production use when there is little change from a stable release.