The issue is that the user table structure is different among the DBs (not a surprise) and moreover that webcal seems (to me) to store date values as integers (have no idea why). Maybe there could be a way to pass appropriate values from one table to another as a nuBuilder user is created, thus automatically creating a user for the calendar application.
This could boost nuBuilder as a tool for managing every database-related application that requires a multi-user schedule, a critical functionality for a lot of activities/jobs.
I'm trying to integrate webcal on a nubuilder project of mine, but I'm not confident in coding (not a professional, informatics is an hobby to me); I believe that this functionality could bring more users like me and programmers as well finding a more comprehensive framework.
In future I'm willing to try the same trick with the Orthanc framework, a professional server application for DICOM files (medical imaging): it would be great if you'd give it a look as well
Keep up with the good job! Happy new year!