First, let's take a brief look at the features of the project. First and foremost is software inventory and management. Through the use of software "channels", you control what package are available to which clients. You can use this functionality to move software between development, QA, and production, for example, and not have to have multiple copies of the software in various yum repositories if that is how you've managed software up to this point.
Another advantage of using a management tool such as Spacewalk instead of various yum repos is that you have a centralized view of packages that are on a given system, and an easy way to get systems that are out of compliance easily up to date, without even logging in to the host.
Have you ever needed to compare the package sets of two systems, perhaps because one was behaving eratically and the other one was working fine, and you couldn't tell the differences between the two systems? Spacewalk makes it trivial to compare AND reconcile differences between two systems with the click of a button.
Tired of deploying configuration files by hand to multitudes of machines? Through the use of configuration channels, that's no longer something that you need to spend your time doing. Unlike some configuration tools, both global configurations may be specified, which are applied to any system subscribed to the channel, as well as local overrides to those configuration files at the individual system level.
All of the items listed above can either be scheduled for execution as soon as the machine checks in with Spacewalk, or at some arbitrary time in the future. The architecture is that of a 'pull' - the end systems run a daemon that periodically checks in with the Spacewalk server. Also available is functionality, enabled via a Jabber server, to schedule actions for more precise time-based execution.
Most of the functions of Spacewalk that can apply to more than one system can be executed via the System Set Manager (SSM) in order to have the same change applied to a set of systems at the same time.
Some of the short term goals for Spacewalk include the integration of Cobbler to replace the existing provisioning functionality and migration of the backend database to something open source. Some longer term goals include integration of Func (possibly to replace/supplement OSAD), and possibly using Puppet for the configuration management functionality. A very short term goal is to get Fedora, CentOS, and RHEL manageable within the same organization - there are currently some technical limitations to this happening. In the meantime, however, these are manageable in separate organizations.
The opening of the Satellite codebase allows the usage of Spacewalk, and the downstream RHN Satellite product, as an integration platform for best-of-breed open source management technologies, rather than having to grow all of the functionality internally within Satellite itself. It also allows users of the commercial product a lot of input into the direction of where the product goes, and if a feature is a priority for them, they are free to implement it themselves upstream!