MobileSubstrate is a Free jailbreak tweak in Cydia developed by Saurik.  He is the person responsible for starting Cydia, Winterboard, and many other tweaks.   He has developed many great tweaks in Cydia.  MobileSubstrate is like a “safe mode” for the iOS device.  Should the device crash it will restart in safe mobe through MobileSubstrate.  [...]