iSHSHit is described as 'allows you to backup your SHSH blobs from Apple directly on your iDevice for later downgrading'. There are five alternatives to iSHSHit for Mac, Windows, Linux, iPhone and iPad. The best alternative is redsn0w, which is free. Other great apps like iSHSHit are TinyUmbrella (Free, Open Source), PkgBackup (Paid), iFaith (Free) and checkra1n (Free).
redsn0w is a utility that will jailbreak your iPhone or iPod Touch, allowing it to run apps that are not approved by Apple. redsn0w can perform an untethered jailbreak of iOS 5.0.1 for all iPhones, iPod Touches, and iPads.
TinyUmbrella saves the "SHSH blobs" of your Apple device (i.e. iPhone, iPod, or iPad), allowing you to bypass Apple's servers and downgrade your firmware through iTunes, whenever you want. Your device does NOT have to be jailbroken for TinyUmbrella to work.
iFaith is a program that can save the SHSH blobs of the current version of iOS that's running on your jailbroken iPhone. It will work any version of iOS, whether or not that version is still signed by Apple.