Stannp.com is a free app that allows users to quickly and easily create their own custom-made postcards. The company provides the Stannp API that allows developers to integrate this tool into other applications. By snapping a picture or using an existing image, the user has the option to customize the image with fun effects and add the finished product to their Facebook wall, email it to a friend or have it turned into a real postcard to be posted the same day.
Defensio, the anti-spam service, offers an API that can be integrated into blogs and web sites to fight spam comments and other unwanted spam (details at our Defension API profile). The service appears to be run by a small team, and is similar in purpose to Akismet, the much larger spam filtering service from Automattic (which powers WordPress.com), who also offer an anti-spam API.
A brand new iOS messaging/social app called Peach has rocketed in popularity since launching last Friday. A developer has reverse engineered the Peach API and created clients for Swift and Mac. The clients have been posted on GitHub for developers interested in using the undocumented Peach API.