Vlad Zamfir, a researcher at Ethereum and co-founder of Smart Transaction (STXN), created a "time machine" that allows Ethereum users to reverse "smart contracts" on the blockchain, reducing the immutability of certain transactions. Smart contracts also allow users to set specific conditions for transaction time and execution. Similar to the way Gmail allows users to cancel sending emails, this feature will be supported on blockchains compatible with the Ethereum virtual machine.