The key difference between Microsoft Dynamics GP vs Dynamics 365 Business Central is that GP was built to be on premise and Business Central was designed for the cloud
Microsoft Dynamics GP Overview
Microsoft Dynamics GP, also known as Great Plains Accounting Software, is a Microsoft Accounting Software specially designed for small to medium-sized businesses. Different applications for financial management, human resources management, manufacturing planning, supply chain management, field service, business intelligence, collaboration, compliance, and IT management are provided by Microsoft Dynamics Accounting. Microsoft Dynamics GP also can be seamlessly integrated with hundreds of third-party applications from independent software vendors. This Microsoft Great Plains Software works well with Microsoft Windows and .NET frameworks. This system is compatible both on-site or on a monthly hosting basis.