This page is talking about a project called iRuby, which I assume is unrelated or successor. The repository this page links had a 0.8.0 release exactly one month ago.

The same org does also have a sciruby project that hasn't been touched in 8 or 9 years like you say.

While the example-notebooks repo you've mentioned is not actively maintained it looks like the IRuby kernel used by Jupyter still is maintained: https://github.com/SciRuby/iruby