at command is used to schedule commands to be executed once at a particular time in the future. More precisely, it reads a series of commands from standard input and collects them into one "at-job" which is carried out at a later date. It is found in the Unix family of operating systems and other flavors as well.
at can be made to mail a user when done carrying out a scheduled job of theirs, can use more than one job queue, and can read a list of jobs to carry out from a file instead of standard input.
It uses a daemon, atd, which waits in the background periodically checking the list of jobs to do and executing those at their allotted time on behalf of at. It can be made to only run scheduled jobs if the system's load average is below a certain value.