South African open source ECM developer Knowledge Tree recently announced that their package has seen more than 380,000 downloads. Of course, veterans of open source projects will concede that downloads doth not a production implementation make. However, Knowledge Tree has sold the commercial version of the tool to such clients such as Bank of Scotland and the European Space Agency. Doubtless one of the appeals of the package is that it's written in PHP -- common enough among Web CMS tools, but quite rare for a document management platform.
It seems amazing that just a few years back there were no credible open source ECM vendors, and now we have at least three vibrant offerings, Nuxeo, Knowledge Tree and Alfresco, with more emerging. Throw into this the ECM-in-a-Box offering from InfoGrid, and the array of SaaS offerings hitting the market and one has to conclude that buyers' choices have never been wider. The ECM marketplace clearly remains far from mature.