Tiny Umbrella 4.21.02 for Windows, Mac OS X and Linux has been released by its developer just a little ago and is available to download. A few days ago, he announced the release of a new TinyUmbrella version which will allow you to restore your iDevice without iTunes. Though it is not that version of the software, TinyUmbrella 4.21.02 allows you to save Apple TV SHSH blobs on iOS 4.2.1.
This is the official description from the site :
UPDATE: By popular demand I’ve updated 4.21 to support Apple TV 4.2.1 SHSH’s. I’m still working on the new iteration of the Tiny family. Stay tuned!
Download TinyUmbrella 4.21.02 from here