Google has just announced that the default quota for the Calendar API v3 has been raised to 1 million requests per day, 10 times higher than the original quota. Applications that use the Google Calendar API can now accommodate 10 times more users without having to request an increase to their allowed daily quota.
Google updated the Calendar API in September, adding several new features and improvements, including push notifications support, new sync tokens, fields for custom colors and compatibility changes with Google+ events. According to an article written by ProgrammableWeb's Eric Carter, "The Google Calendar API, version 3, is based on a new API infrastructure that renders the API incompatible with older versions built on top of Google Data Protocol (GData). Instead of GData, version 3 is JSON based."
Calendar API v1 and v2 were shut down on Nov. 17 in accordance with the company's deprecation policy. A migration guide is available for developers looking to update their applications from v2 to v3.
Developers interested in using Calendar API v3 can find detailed information on the Google Developers site.
See also ProgrammableWeb's article about how the new Google reCAPTCHA API solves the identity verification puzzle, an article about whether you should develop for Android or iOS first, and an article about the the Navigation Transitions API for Chrome.