You can use the FinanceConnector to contact Daylite with a bunch of different billing systems. The current systems that can get connected to Daylite are QuickBooks and sevDesk.
The link below will take you to a page that provides an overview of all billing systems that can be integrated with Daylite:
About QuickBooks Integration
What is the FinanceConnector?
How do I configure the FinanceConnector?