Check out dev.outlook.com!
In addition to all of these investments we wanted to make it even easier for developers to build add-ins and applications that integrate with Outlook and Exchange by creating a single site for the Outlook platform with tutorials, references, support and feedback forums, SDK’s, and helpful tools. That site is http://dev.outlook.com – we encourage you to check it out and give us your feedback.
We are going to be iterating on the content quickly over the upcoming weeks, adding getting started guides, code samples, and useful information on the rollout of the extensibility platform to Outlook.com. So bookmark it and check back often to see what we have added.
http://dev.outlook.com is an Outlook centric-view on Office extensibility. If you are interested in the overall Office platform make sure to check out http://dev.office.com where you will find information on the entire Office platform.