If you are new to Nuxeo, they have a legitimate claim to being the first open source ECM company. Their primary geographic focus is in France and they are less well known in the US. Nuxeo's original ECM product (which combined Document Management, Collaboration, and Web Content Management) was written on the Zope platform. In 2006, they ported their product (then called CPS for Collaborative Portal Server) to a Java stack (using JBoss Seam). Long time readers of this blog may remember me being skeptical of whether they could pull it off. It turns out that they did a great job with the migration and have been aggressively pushing the platform forward.
Like, Alfresco, Nuxeo's experience and customer base leans towards the document management side of ECM. Web content management is a newer focus that is (I think) well timed as more companies are looking for ways to rapidly build internally and externally facing content centric web applications.