I would like to recommend Java-based Gen GST software for return filing & billing. It has multiple features such as unlimited return filing, GST billing for regular and RCM dealers, import and export facility, input tax credit, backup, security, etc. SAG Infotech offers a free trial version of 20 working hours.
Some Important Features of Gen GST Software
Unlimited GST return filing with DSC/EVC (GSTR 1, 3B, 4, 9, 9A, 9c etc.)
Automatic Detection of Errors
User-wise Rights, Return & Invoice Status
GST billing for Regular & RCM (Reverse Charge Mechanism) traders
GST E Way Bill generation
All Options for e-Payment of Taxes
Import & Export Data Facility