Zope

Application server software, written in Python, for building content management systems, intranets, and portals. Free of charge.

The link address is:
http://www.zope.org/

If you can read this text, it means you are not experiencing the Plone design at its best. Plone makes heavy use of CSS, which means it is accessible to any internet browser, but the design needs a standards-compliant browser to look like we intended it. Just so you know ;)