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.
Here's how Context.io described the service in its announcement post:
Context.IO is an email API that opens up instant access to years of important data: conversations, business information, attachments, etc with one simple HTTP call. Our API allows you to build apps that leverage this data in a way that wasn’t previously possible without a series of complex sequences of IMAP requests.
Context.IO is a RESTful service that provides developers easy access to the information inside emails, including attachments. One of the neatest tricks it has is a facility to compare two attachments side by side, marking the differences, for use something like a versioning system.
TheNextWeb described another fun use of the API:
In November during hackMTL, a one day hacking event held in Canada, a developer used DokDok’s API to create an app that transformed his inbox into a visual representation of his social graph. DokDok says that Nicholas Kruchten’s app is the most unexpected case use for the API so far.
A PHP library for using the API is already available on github.
Like many APIs, you'll need a developer key to get in on the fun. The service is currently in closed beta, but you can request access on the site.