The MacPorts project (http://www.macports.org/) has for years been packaging a long list of open source software packages for Mac OS X, and they have packaged Node. After you have installed MacPorts using the installer on their website, installing Node is pretty much this simple:

$ sudo port search nodejs
nodejs @0.10.6 (devel, net)
 Evented I/O for V8 JavaScript

nodejs-devel @0.11.2 (devel, net)
 Evented I/O for V8 JavaScript

Found 2 ports.
--
npm @1.2.21 (devel)
 node package manager
$ sudo port install nodejs npm
.. long log of downloading and installing prerequisites and Node

Homebrew is another open source software package manager for Mac OS X, which some say is the perfect replacement for MacPorts. It is available through their home page at http://mxcl.github.com/homebrew/. After installing Homebrew using the instructions on their website, using it to install Node is as simple as this:

$ brew search node
leafnode node
$ brew install node
==> Downloading http://nodejs.org/dist/v0.10.7/node-v0.10.7.tar.gz
######################################################################## 100.0%
==> ./configure –prefix=/usr/local/Cellar/node/0.10.7
==> make install
==> Caveats
Homebrew installed npm.
We recommend prepending the following path to your PATH environment
variable to have npm-installed binaries picked up:
 /usr/local/share/npm/bin
==> Summary
/usr/local/Cellar/node/0.10.7: 870 files, 16M, built in 21.9 minutes

While it's still premature for Linux distributions or other operating systems to prepackage Node with their OS, that doesn't mean you cannot install it using the package managers. Instructions on the Node wiki currently list packaged versions of Node for Debian, Ubuntu, OpenSUSE, and Arch Linux.

See: https://github.com/joyent/node/wiki/Installing-Node.js-via-package-manager

For example, on Debian sid (unstable):

# apt-get update
# apt-get install nodejs # Documentation is great.

And on Ubuntu:

# sudo apt-get install python-software-properties
# sudo add-apt-repository ppa:chris-lea/node.js
# sudo apt-get update
# sudo apt-get install nodejs npm

We can expect in due course that the Linux distros and other operating systems will routinely bundle Node into the OS like they do with other languages today.

The nodejs.org website offers prebuilt binaries for Windows, Mac OS X, Linux, and Solaris. You simply go to the website, click on the Install button, and run the installer. For systems with package managers, such as the ones we've just discussed, it's preferable to use that installation method. That's because you'll find it easier to stay up-to-date with the latest version. However, on Windows this method may be preferred.

For Mac OS X, the installer is a PKG file giving the typical installation process. For Windows, the installer simply takes you through the typical install wizard process.

Once finished with the installer, you have a command line tool with which to run Node programs.

The pre-packaged installers are the simplest ways to install Node, for those systems for which they're available.

Chocolatey Gallery is a package management system, built on top of NuGet. Using it requires a Windows machine modern enough to support the Powershell and the .NET Framework 4.0. Once you have Chocolatey Gallery (http://chocolatey.org/), installing Node is as simple as this:

C:\> cinst install nodejs