This repository is used to create an HSQLDB binary that includes patches which have not yet been released.
There is currently only one patch difference related to silent option which is not working:
https://sourceforge.net/p/hsqldb/bugs/1456/
Once the fix is included in an HSQLDB release, the Scheduling project can switch back to an officially supported release version of HSQLDB.
You simply need to move to build/ folder and execute the following command:
$ ./gradlew hsqldb
The last command will output a file named hsqldb.jar in lib folder.