For GST Billing there are a number of options to select from. There are both Free and Paid Software services and scripts to help you generate bills in few minutes.
Ewaybill.net is one such free software or script that helps you generate a bill in PDF format.
There is no registration required and the service is free. However, no data like your business or company name, address and details are stored.
So each time you want to generate a bill, you have to enter all details. If you want to save some of your details, like the address or recipient, you can request for the same.
As Free GST Bill generator, the software doesnot file your GST on government portal. It only generates a bill as per the standard GST Bill format.