Joyent Slingshot allows developers to deploy Rails applications that work the same online and offline (with synchronization) and with drag into and out of the application just like a standard desktop application. Check its two-minutes tutorial to get a feel of how you can make it work.
Earlier this month, they finally released Slingshot to the public. They also celebrated it with a contest offering their $1250-worth Accelerator for the prize.
We've posted about Slingshot before it was officially released. In addition to stabilizing the overall framework, they also have made several enhancements, including the decision that they will open source the technology (planned for June).
You can find more information on their developer wiki.

Comments
Mat Schaffer ·
This is really exciting. And timely considering how Apollo is catching on. Nice work Joyent!
Hendy Irawan ·
Dear Mat,
I truly agree with you, Mat.
Between Adobe's (which can work with Ruby), Microsoft Silverlight (DLR, hence works with "any" scripting language including Ruby), and Slingshot, the choice is yours.
Java also has made progress in this offline/online dilemma, demonstrated by Zimbra. And of course the several-years-old Java Web Start. :-) JRuby has been very helpful in bringing the Java and Ruby camps together.