Affectiva's emotional measurement API has been around for a couple of years now. Affectiva has seen adoption by marketers, publishers, gaming companies, and chat services. However, Affectiva believes it can greatly expand the use case scenarios by offering its service at no charge to startups.
We have covered the BigML API before because of its innovative use of machine learning through an API tied up with very easy to use interface. Think of it as Google Prediction API but without a black box algorithm, and with enhanced real time data visualizations and a much better user interface and crisper documentation.