BitNami RubyStack provides a fast, easy way to develop and deploy Ruby on Rails applications. It includes Ruby, Subversion, MySQL, SQLite, ImageMagick, and several Ruby Gems, and will optionally install Apache 2.2 with rewrite and proxy support. It supports Windows, Linux, and OS X, so you can share the same Rails environment on multiple platforms.
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.
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.
CTL is a cross-platform control dispatching tool that makes it easy to automate any kind of distributed systems management or application provisioning task. Rather than writing complex and error-prone scripts that over utilize "for loops", CTL handles the network dispatching for you and allows you to focus on the actual management tasks you need to accomplish. In addition to being a dispatching tool, CTL comes with pre-built cross-platform utilities so you don't have to script actions like file distribution or process and port checking. You can also write your own custom utilities and share them with others in your organization. Custom utilities are defined in XML, and your scripting can be done in multiple scripting languages (Perl, Python, etc.), *nix shell, Windows batch, and/or Ant.