Today AppHarbor is unveiling our add-on program. As of right now, you can add third-party services from MongoHQ (MongoDB), Cloudant (CouchDB), Redis To Go (Redis), Mailgun (email sending and receiving) and Memcacher (memcached). We have wanted to offer these kinds of services on AppHarbor for a long time, and we think that letting third party service providers onto the platform is the best way to get developers access to a wide selection of high-quality services.
Adding an add-on to one of your applications is very simply: Simply select 'Add-ons' from the application menu on appharbor.com/, find the add-on you want and then add it. This causes AppHarbor to provision the resource with the add-on provider so that it is ready for your application to use. The next time you deploy your application, AppHarbor will inject the required configuration information into your application so that the service can be consumed. You can find more detailed information on how that works for the various add-ons in the add-on section of the knowledge base.
We hope to soon offer many more exciting services as add-ons on AppHarbor. If you have an idea for a service that you think should be available (or if you think you can do a better job of providing a service already offered), you can start building an add-on right now. Our add-on API is based on Heroku's and the documentation is open. Have an idea for an add-on? Drop us a line at firstname.lastname@example.org.