Well over 600,000 developers participate in a topcoder community that not only allows them to expand their development skills, but also gives them access to projects where they can get paid for participating.
Involver launched its Engagement Optimization API last week (read the official release here). Partners are utilizing the API to "optimize their ad spend on social in the way they've been doing across the web for a long time." Although advertising across social networks has been deployed for quite some time, advertisers have had limited tools to track engagement. Facebook Insights is probably most commonly used to analyze social data. When users have required deeper analysis, the advertisers were forced to use highly custom integrations.
Jinni, television and movie taste engine, has expanded its API to include a feature that discovers movies and shows that more than one viewer will enjoy: Watch Together. The Watch Together feature expands the discovery engine API to include social functionality (e.g. makes recommendations based on the tastes of multiple, disparate tastes). Based on multiple profiles of a group that would like to watch a show together, Watch Together makes a recommendation.