JRuby-docker is a set of is a set of Docker images meant to serve as good bases for JRuby. It uses stepsaway/baseimage-docker as it base image and builds & installs JRuby from source.
Each major version of JRuby has its own image and the patch level changes are included in the tag.
The tags for JRuby-docker include the patch level for the major JRuby version, followed by the version of stepsaway/baseimage-docker which JRuby-docker uses for its base image. For example, JRuby 9.4.1.0 on stepsaway/baseimage:1.0.0 would be: stepsaway/baseimage-jruby91:4-1.0.0