Adobe Apollo

For those who aren't familiar with Apollo, I'll start by taking the definition from the Apollo Developer FAQ on Adobe Labs:

"Apollo is the code name for a cross-operating system runtime being developed by Adobe that allows developers to leverage their existing web development skills (Flash, Flex, HTML, JavaScript, Ajax) to build and deploy Rich Internet Applications (RIAs) to the desktop."

Essentially, Apollo is Adobe's initiative to bring Rich Internet Applications from the web to the desktop in a way that uses the best of both worlds. The idea is that developers will be able to bring their web applications offline and take advantage of things a desktop application can do including accessing the file system and drag and drop from the desktop to the application.

In addition, Apollo is going to be cross platform meaning you can build these desktop applications and they will run on PCs, Macs and Linux machines.

Links:
A tour of Adobe’s Apollo project with Kevin Lynch
Apollo in Adobe Labs
Building Killer RIAs - Breeze Video
I Have Seen Apollo and it is Awesome - Ryan Stewart
Apollo by Mike Chambers