 Schroeder's Multics shell was the predecessor to the Unix shell, which is still in use today.Working with Pat Crisman and Louis Pouzin, she also described an early e-mail system called "MAIL" to allow users on the Compatible Time-Sharing System (CTSS) at MIT to send notifications to others about backups of files.Each user's messages would be added to a local file called "MAIL BOX", which would have a “private” mode so that only the owner could read or delete messages.