Sidenote: I wrote this article two months back, at WordCamp US, and am only now getting around to posting it. Sorry for the delay.
A lot of folks got excited and a few got scared. Some folks got a bit confused. But I haven’t heard many folks drawing the parallel and writing the explanation that I’ve cobbled together, so here’s my take on it:
For a while now, there’s been a variety of WordPress apps — iOS, Android, and some defunct ones for Blackberry, Windows Phone, WebOS, and the like. They all interact with WordPress via the existing XML-RPC API. They’re not really extensible for plugins — if someone installs “The Events Calendar,” events don’t start showing up in the app as they would in your traditionally PHP-generated WordPress Admin UI.
Calypso currently mirrors those mobile apps more than anything else, just shifted to a wholly different space. Instead of using the legacy XML-RPC API, which is meant primarily as a way to publish content and has a host of issues (sending user passwords in plaintext with every request, for one), it uses a REST API with far better authentication. Instead of running on mobile devices, it runs either in your web browser at WordPress.com or encapsulated in a Desktop app. But at its core, it’s a self-contained administrative application for WordPress sites.
I feel that the biggest win in releasing the Calypso interface, though, is that it can remedy a situation that’s festered for some time now. The current WordPress mobile apps are maintained by a crew of mobile developers that work for Automattic.
So, it falls to someone to find and hire Mobile developers to maintain the assorted WordPress mobile apps.
This, I think, will mean a significant renaissance of community interest in API-driven apps for maintaining a WordPress site. I also predict that we’ll see a lot of folks passionate about WordPress forking Calypso and tweaking it to make customized apps and distributions for specific clients and use cases — which will only expand further once REST API endpoints ship in WordPress Core, and Calypso migrates to use those, instead of the WordPress.com REST API.