"Jitsi is an audio/video Internet phone and instant messenger written in Java. It supports some of the most popular instant messaging and telephony protocols such as SIP, Jabber/XMPP (and hence Facebook and Google Talk), AIM, ICQ, MSN, Yahoo! Messenger."
Not available for iOS.
The Google Calendar API lets you develop client applications that create new events, edit or delete existing events, and search for events. This document describes how to use RESTful calling style and client libraries for various programming languages (currently Java, Python, PHP, .NET and Ruby) to access and edit Google Calendar data.