Run a program using only idle cycles

 loadwatch forks a child process and only allows it to run when the
 system load meets user-defined parameters. It allows you to specify
 that a program should run only if the load is below a specified
 point, and will stop it when that point is reached. When the load
 falls below a second specified point, the program will be
 continued. The user can also specify the system load sampling period.