Dropbox recently released v2 of its Team Events API. The Team Events API is part of Dropbox Business and allows users to track activity within Dropbox. The API has been completely rewritten from v1, and includes over 300 events that users can access through the activity log.
Online diagramming service Creately opened its Creately API to the public this month, and with some surprisingly innovative features. While providing obvious features to make its service available to outside developers, and several "above and beyond" features, such as easy embedding of diagrams, Creately has done something fairly unique: open up its own, web-based file format for other developers to use.