Is it a free or license
There are two versions of DayPilot for ASP.NET WebForms
DayPilot Lite for ASP.NET WebForms (open-source)
DayPilot Pro for ASP.NET WebForms (commercial)
See also the feature matrix which compares the feature of both versions:
Is DayPilot Lite for ASP.NET WebForms (open-source) free?
Yes, the open-source version is free.