Remedy Toolbox is a Graphical Java client that uses JavaFX.  Java 1.8 and before included JavaFX, but it is no longer included and must be downloaded independently.

The JavaFX libraries are OS dependent, so you'll want to download the right version for your machine.

If using Java 1.8, you can simply provide a command line of

java -jar APLRemedyToolbox.jar

and you should launch without problem.  If using Java 9+, you'll need to download a version of JavaFX SDK from

https://gluonhq.com/products/javafx/

Once downloaded and extracted, assuming you extracted the SDK to

C:\JavaFXSDK

your Java command line looks like this

java --module-path "C:\JavaFXSDK\lib" --add-modules javafx.controls,javafx.fxml -jar APLRemedyToolbox.jar

---------------Command Line Options-----------------

There is one optional command line parameter that can be specified

-db

This allows you to launch the tool against a specific DB file instead of the default APLRemedyToolbox.db.  With this command line you could setup different
db files for different customers, or if you just wanted the db file to be located somewhere other than the tool folder.  In Java 8 the command line would look like

java -jar APLRemedyToolbox.jar -db YourDBFile.db

If the file doesn't already exist, the tool will create it for you

Once you have the tool launched, there is in-app help via a button in the upper right corner with a ? on it.