This image includes the Jenkins build of Waterfall, "a drag and drop replacement for BungeeCord that adds new features, fixes bugs, and improves performance." For more information on the software itself check the GitHub repo for it or its webpage over at the Aquifer website. For information about the original BungeeCord check the BungeeCord Wiki.
All available tags are always listed in Docker Hub, the list below explains the maintained tags:
latest,b158: Latest version of Waterfall.
Previous builds may also be available as tags in the format b<number>, for
example b75.