A whole heap of voice and sms APIs, in a similar vein to twilio / tropo, but seemingly a broader offering, and possibly a later entrant to the market.
Similar to Twilio, send / receive voice & sms via APIs. Doesn't appear to be as quickly evolving as twilio, but free for development use.
Google's CalDAV api documentation. Their calendar service supports some caldav functionality, but not all. Interesting potential for soundclient.
Developer APIs for placing calls and sending SMS messages. Handles both incoming and outgoing, but only sends texts in the US and only has incoming US / Canadian numbers.