The KashFlow PHP SDK by Joel Fielder is available to download, found in the tutorial "Integrating with Kashflow using PHP." References explain how to configure the KashFlow account, interact with the API, handle parameters, and create a sales invoice working with the API.
Xero, cloud accounting software provider, has expanded its Payroll product to integrate with other applications via the Payroll API. The Payroll API allows developers to build add-on apps to work alongside Xero products, or integrate Xero functionality into existing apps and workflows. Xero's target audience remains in the SMB space who typically cannot afford massive onsite, dedicated ERP and accounting software packages.