Puppet lets you centrally manage every important aspect of your system using a cross-platform specification language that manages all the separate elements normally aggregated in different files, including users, cron jobs, and hosts, along with obviously discrete elements like packages, services, and files. Its simple declarative specification language provides powerful classing abilities for drawing out the similarities between hosts while allowing them to be as specific as necessary, and it handles dependency and prerequisite relationships between objects clearly and explicitly.
Elektra is a universal hierarchical configuration store, similar to GConf and the Windows Registry. It allows programs to read and save their configurations with a consistent API, and allows them to be aware of other applications' configurations, leveraging easy application integration. While architecturally similar to other OS registries, Elektra does not have most of the problems found in those implementations. Elektra includes a library, an API, and commandline and GUI tools for administration tasks.
Einarc is a unified storage RAID command line interface and an API that provides management for various hardware/software RAID devices, uniting them all in a single paradigm. Einarc works as a translator that makes it possible for a user to control all these devices using simple terms like "physical disc", "logical disc", "adapter", etc., while transparently converting these requests to proprietary RAID paradigms.
acoc is a regular-expression based colour formatter for programs that display output on the command-line. It works as a wrapper around the target program, executing it and capturing the stdout stream. Optionally, stderr can be redirected to stdout, so that it, too, can be manipulated. acoc then applies matching rules to patterns in the output and applies colours to those matches.
The Marionette Collective (mcollective) is a framework to build server orchestration or parallel job execution systems. It uses modern technologies and concepts that make it ideal for large and cloud-based infrastructures. It's specifically geared towards systems administration tasks, but can be seen as a generic framework too.
Facter is a simple cross-platform library for determining basic facts about an operating system, like the operating system name, IP address, or MAC address. It supports multiple mechanisms for resolving a given fact, and these mechanisms can be restricted to only working on specified operating systems or operating system releases.
Ruby/Password is a set of useful methods for creating, verifying, and manipulating passwords. It includes an interface to CrackLib, a library commonly used for checking password strength. It is intended to be used by system administrators who need to write Ruby programs that prompt for, generate, verify, and encrypt passwords.