San Francisco-based Pantheon opened its doors to the public today after a year building its Web development platform for Drupal sites. (Drupal is an open-source content management system). Pantheon is a combination of a Web development tool in the cloud and a Web hosting and management service. Companies can develop, test, host, and manage their websites on Pantheon It is all based in the cloud, and the service is free for developers. Once you make a site go live, it costs $100 a month. The company raised a $1.3 million seed round a year ago from First Round Capital, Baseline, Floodgate, Founder Collective, and Heroku founders James Lindenbaum, Adam Wiggins, and Orion Henry. You can think of Pantheon as a Heroku for Drupal sites in that it puts the web development environment in the cloud. Founder and CEo Zack Rosen has simpler description of what Pantheon offers. " You can get an enterprise-complete website for your organization with the level of polish of a consumer-grade site." The reason so many corporate and organization websites look out of date is because they are built with expensive, proprietary Web development software that fails to keep up with what is going on in the consumer Web. Pantheon offers a platform for developing custom sites. It is built on top of Drupal, which is fast and versatile, but Pantheon makes Drupal development more accessible. Pantheon makes it easy to deploy different versions of a site on test servers and the live site, as well as backup servers. Some Websites are already running on Pantheon. Customers include the United Nations Global Pulse site, USC Marshall School of Business, and online publisher TheFix. The unique twist that Pantheon brings to the table is that it is not just a development environment. Once a site is ready to go live, it runs the site as well. "We carry the pager for your website if anything goes down," says Rosen. It also has done the hard work to optimize Drupal so that every site runs really fast. Pantheon itself runs on Rackspace Cloud. Why not Amazon Web Services? "Rackspace is much faster at running Drupal than Amazon," says Rosen. But the backend is built to make it portable if Pantheon ever decides to move.