capybara-webkit depends on a WebKit implementation from Qt, a cross-platform development toolkit. You'll need to download the Qt SDK to build and install the gem.
If you're on Ubuntu, you can install the libqt4-dev package. On Linux platforms, capybara-webkit requires an X server to run, although it doesn't create any visible windows. Xvfb works fine for this.
Add the capybara-webkit gem to your Gemfile:
The capybara WebKit driver was written by Joe Ferris, Tristan Dunn, and Jason Morrison from thoughtbot, inc.
The names and logos for thoughtbot are trademarks of thoughtbot, inc.
capybara-webkit is Copyright © 2011 thoughtbot, inc. It is free software, and may be redistributed under the terms specified in the LICENSE file.