For information on how to install applications on FreeBSD, check out the FreeBSD Handbook – Installing Applications: Packages and Ports.

FreeBSD has a set of tools that automate installing and upgrading software called portupgrade. What’s even better is, it can be configured to use pre-compiled packages when available.

Update your ports tree:

  # portsnap fetch ; portsnap update

Note: If you need to initialize your ports tree for the first time, portsnap will ask you to run ‘portsnap extract’

Install portupgrade tools:

  # pkg_add -r portupgrade

Install Ruby on Rails:

 # portinstall -PR rubygem-rails 

Note: This will install rails and any dependencies. It will also allow you to choose which database bindings you would like to install.

The -P means use packages when available.
The -R will upgrade any dependencies that are already installed, that are out of date.

If you want an interactive mode use: -i
To force the use of packages use: -PP

Resources

FreeBSD Handbook
FreeBSD Handbook – Installing Applications: Packages and Ports

FLPR is a blog that covers the FreeBSD/lighttpd/PostgreSQL/Rails web development stack. It’s a great source of information on using Rails with FreeBSD.
2006-08-06: To bad it’s gone.
2007-01-01: http://web.archive.org/web/*/http://www.flpr.org/
2007-04-05: ‘No pages found’ for both http://www.flpr.org, and http://flpr.org??? oh boy… How about an archive…. for web.archive.org’s copy of www.flpr.org?