The Vero Python SDK by Ryan Wilson-Perkin allows to access the API to implement email platform features such as users, subscriptions, and events. Usage demonstrates how to create an instance and interact with users.
DokDok, a Montreal-based startup, has had an email attachment management application on Google Apps some time. To make this work, it made an API to use internally that intelligently uses email accounts as if they were datastores. Recently, the company announced that this API would be renamed Context.IO and available to all.
Take Twitter, add its concepts as a platform to banking and you get BankSimple, the unlaunched startup that you will definitely want to keep your eye on. BankSimple is a new take on online banking created by Twitter's former API guy, Alex Payne. BankSimple is aiming to create a banking platform, much as Twitter became a messaging platform.
The Streak API integrates its client relationship management (CRM) platform into other applications like MailChimps and Wufoo. The API's webpage reveals that it requires an API key and uses HTTP Basic Auth. The request format supports Create, retrieve, update, and delete (CRUD) with response in JSON. The purpose of the API is to manage CRM relationships through your application.