Simian is an enterprise-class Mac OS X software deployment solution with App Engine-based hosting to scale with the needs of your growing enterprise, and a future proof client based on the Munki open-source project.
Here are some example features of Simian:
Deploy new or updated software by targeting a single Mac or tens of thousands.
Push security patches, whether the Mac is on an internal network/VPN or not.
Force mandatory installation of some packages, while allowing others to be optional.
Tightly manage Apple-provided updates.
Scale without deploying and maintaining additional server infrastructure.
Obtain reports on all of this and the fleet overall.
Much of this and more is due to the outstanding work of Greg Neagle and the Munki community. To read more about the other features Munki offers please visit the Munki code.google.com project page.

munki is a set of tools that, used together with a webserver-based repository of packages and package metadata, can be used by OS X administrators to manage software installs (and in many cases removals) on OS X client machines.
munki can install software packaged in the Apple package format, and also supports Adobe CS3/CS4/CS5 Enterprise Deployment "packages", and drag-and-drop disk images as installer sources.
Additionally, munki can be configured to install Apple Software Updates, either from Apple's server, or yours.
munki is currently in use at organizations all over the world, managing software for thousands of Macs.

Chef is a systems integration framework, built to bring the benefits of configuration management to your entire infrastructure.