Yes. The code is freely available under the terms of The BSD License.
Download from https://github.com/hebcal/dotcom.
hebcal.com depends on https://github.com/mjradwin/hebcal, currently a fork of the mainline https://github.com/hebcal/hebcal repository.
The only difference between the main hebcal/hebcal program and the mjradwin fork is the use of a different sunrise/sunset algorithm that supports Olson tzdb timezones