Offernaut is a personal tool that Dmitrii Sherstianykh runs for his own job search. It keeps track of the jobs he applies to and of the replies employers send him.
With his permission, it reads the messages in his own Gmail account that are replies to his job applications, so that each reply shows up next to the job it belongs to. It only reads; it does not send, change or delete mail.
It is not offered to anyone else, and no one else signs in to it.