I have Java 8 Update 281 installed and I just downloaded the most recent version of oStorybook for the Mac.
I also set my Mac so I can open  Unidentified Developer Apps & Allow Downloads From Anywhere On Apple Mac.
Yet when I open the oStorybook-5.04.05d-macOSx.tar.gz to Contents>Resources>Java> and attempt to open oStorybook.jar using the Java Launcher, nothing happens!!!
Do I need anything else to make this work, for example, a JDK or JDE?

The file you downloaded is a tar.gz, which means that it is compressed. Here is what I recommend you to do:
- create an application subfolder (e.g. /oStorybook) in your home directory.
- unzip and untar the downloaded file with the tools available on MacOS.
- look for the file oStorybook.jar in the sub-folder and click on it.

MacOS will recognize that it is a Java file and will execute it.

I'm sorry, I don't have, and never had, a Mac to be able to say more.

Translated with www.DeepL.com/Translator (free version)

Thank you very much; that worked!
I appreciate your help.