System management software is a nebulous term; the discussion here is about software to provision new servers, manage packages, control updates, and monitor servers, all from a central location. This does not necessarily include server hardware inventory, software build management, and other related tasks.
The Red Hat Network is a perfect example; Spacewalk is the open-source version of the Red Hat Network Satellite. Spacewalk has been out for a while, and recently released version 0.7. Originally, Spacewalk required Oracle as the back-end database; they may have been able to remove this dependency (replacing Oracle with PostgreSQL). The CentOS Wiki has a very nice HowTo describing how to install and run Spacewalk.
However, before implementing Spacewalk 0.7, note that Lee Verbern notes that the 0.7 client is broken (rhnsd does not work properly). The problems should be fixed in the next release.
Canonical’s Landscape is a counterpart to the Red Hat Network and is available for Ubuntu systems. Like the Red Hat Network, Canonical’s Landscape is a commercial product and closed source. Canonical has a blog for Landscape news, but the blog hasn’t been updated since November 2009. The Landscape project has a nice page with links to descriptions, tours, frequently asked questions, and more.
The blog WorkswithU has a nice article describing Landscape (albeit from February 2009).
Amazingly, the Canonical Landscape team even has a YouTube account with many valuable videos describing Landscape as well as many tutorials. They have a video introduction to Landscape you might want to see.
Finding an open source provisioning tool (outside of Spacewalk) is difficult; these tools are not common nor are they used by the average user.
One apparently powerful tool seems to be ControlTier, although it leans more towards package (and service) management than provisioning. ControlTier seems to be extremely flexible, allowing you to write scripts to interface with a variety of products and systems. ControlTier also has a blog, though it hasn’t been updated since November 2009.
I think I’d like to try ControlTier with Puppet; in particular, learning Puppet would be a good thing. I’ll report my experiences.