[Bertrand]

Thanks DNSB.

Your 1st link is the version (September 2021, almost 3 years) that I had found.

On the other hand, I hadn't seen the other page. Lots to explore.

Originally Posted by DNSB

There is an old version from 2022 at /readium/r2-testapp-kotlin/releases/.

You can also take a look at the Other toolkits related to Readium page which lists quite a few apps based on the Readium Mobile toolkit.