The Rocker Project provides two key sets (or "stacks") of containers which are non-overlapping by a combination of design, focus, and historical evolution. See the discussion of images for a more complete description beyond the brief sketch here.
The rocker-versioned stack provides versioned and time-stamped builds; these are also the basis for builds providing images with the tidyverse, with RStudio and Shiny, with a geospatial focus as well as with a machine-learning focus.
The r-base stack contains the r-base image as well as builds using r-devel or specific configuration. The r-base image is based on Debian and takes advantage of its broad and generally current 'testing' distribution. Images based on Ubuntu ("r-ubuntu") have also been added to take advantage of the c2d4u repo; on top of this image with bspm support ("r-bspm") were added. The initial r2u container builds are on top of these containers. While some of the Ubuntu containers are still updated at each Ubuntu releases, a focus on the two most-recent LTS releases has also been helpful.
We considered streamlining and altering some of these r-base containers but found that removing features may affect some users. So at least for the time being the existing containers remain.
Since its start in May 2022, the r2u Project has proven to be both useful and popular. Making it part of Rocker is a natural next step.
The initial eddelbuettel/r2u containers have been layered on top of r-bspm and r-ubuntu. For r2u in Rocker we have decided to start directly from Ubuntu LTS containers. We used this opportunity to rewrite the Dockerfile with fewer layers resulting in builds that are faster (and simpler) to run, and also result in smaller containers. These rocker/r2u can be used where the existing eddelbuettel/r2u containers are, and will likely be uploaded under the existing tags.