The Erply C# SDK by Erply is available for download fro the official site. It allows API interaction to access inventory, products, customers, webstore, management, documents, and reports. Requests and responses available in HTTP/POST and JSON/XML respectively.
When Yahoo! shut off a stock quote service that developers were relying on -- albeit anonymously -- developers erupted with disappointment and anger. But those developers were probably trespassing on the service and Yahoo! had no way to notify them of the shutdown. Maybe a standard can fix that.