Started by Thomas Hatch. Released under the Apache 2.0 license.
A good comparison of open-source configuration managements systems: [http://en.wikipedia.org/wiki/Comparison_of_open_source_configuration_management_software]
Thomas Hatch is also working on a project called butter that sits on top of salt for more complex operations such as cloud provisioning.
simplicity - At it's heart, salt is about making it easy to execute commands on a remote server...and fast.