Nexmo offers a series of cloud-based communication APIs that make it easy to integrate reliable communication services into any application. This tutorial by Tim Lytle on the Nexmo blog shows followers how to build a simple text message group chat using the Nexmo SMS API and PHP.
Geeklist offers developers an online haven to present their work, connect with other developers, and gain credit for achievements. Geeklist's lean staff proudly states that Geeklist was "[b]uilt by developers, for developers... we make geeks lives better every day." The API allows developers to create their own applications and services and retrieve any needed data from the Geeklist database. The API has remained in private beta since the Geeklist's original launch, but will open to the public with a 48-hour hackathon from November 30 - December 3.
Publr.com is a free blogging service with a few innovative features. It allows posts of various types, including your typical text, but also including maps, videos, chat transcripts, and links. Its site has a pretty good typical web interface for such things, and there are both first-party and third-party applications to use to post. Those third-party applications use the Publr API.