Linux queuing system

For a single machine, the at command is probably enough. It allows you to configure your task to only run when your resource usage is low (<0.8) using the -b (batch) switch, or you can specify priority using the letters a-z.

example:

at -q b now /home/myname/script.sh

equivalent to:

batch /home/myname/script.sh

For clusters, use GNU Queue.