Hi sir i have already build Accounting application support GST you will get modern UI . i can provide you all the source code.
1. Account group,Account ledger, balance sheet, trial balance,profit and loss a/c, day book, bank book, cash book, payment voucher, receipt voucher, journal entry, contra entry.
2 sales purchase and all the inventory management.
3 Product barcode generation and also sale and purchase can done by barcode reader machine.
4. different kind of reports and latest you will get GSTR-1 and GSTR-2
Thank you
If you interested then please ask for demo