Engine is a set of private, in-house tools built and run by Salt Lake Consultants LLP for its own internal use. The tools help the owner organise his own email, receive his own alerts, and keep backups of his own data. They are not offered to the public and have no other users.
The Google-connected tools
Engine Mail Reader reads, with read-only access, messages in the owner's own Gmail account from a short list of senders he has chosen, and can add a copy of an internal notification message to the same mailbox.
Engine Backup uploads backup files of the owner's own data to a folder in the owner's own Google Drive. It can see only the files it creates itself.