Mesos is a cluster management platform for running multiple distributed applications or frameworks on a cluster. Mesos can intelligently schedule and run Spark, Hadoop, and other frameworks concurrently on the same cluster. Spark can be run on Mesos either by scheduling individual jobs as separate Mesos tasks or running all of the Spark code as a single Mesos task. Mesos can quickly scale up to handle large clusters beyond the size of which you would want to manage with the plain old SSH scripts. Mesos, written in C++, was originally created at UC Berkley as a research project; it is currently undergoing Apache incubation and is actively used by Twitter.
The Spark web page, http://spark.apache.org/docs/latest/running-on-mesos.html, has detailed instructions on installing and running Spark on Mesos.
