They can be divided into different categories based on customer type, sales model, market sectors, etc.
By target audience: Peer-to-Peer (P2P); Business to Customer (B2C); Business to Business (B2B).
By focus: vertical, horizontal.
On the management approach: ungovernable; slightly manageable; fully manageable.
By products: products, services, projects, hybrid.
By interaction: internet commerce, online-to-offline.