Alfresco pounced on that SharePoint protocol that the European Commission forced Microsoft to disgorge and turned up Thursday with what it claims is the first fully compatible open source alternative to Microsoft SharePoint, one of the fastest-growing and stickiest products in the Microsoft arsenal.

Alfresco calls its new widgetry Alfresco Labs 3 and says it will replace the old freebie Alfresco Community that’s reportedly been downloaded some 1.3 million times, essentially producing maybe 500-600 paying customers for Alfresco including folks like FedEx, the New York Stock Exchange, Sony Pictures and KLM.

SharePoint, on the other hand, is supposed to be on hundreds of thousands of servers and have some 80 million users, producing some $1.2 billion in revenue along with 35%-a-year growth.

According to Alfresco CTO John Newton, who in a previous life was the co-founder of Documentum, that other ECM house that EMC now owns, SharePoint is the ultimate lock-in. It forces customers to use Windows, Office, of course – SharePoint is the only system designed to work with Office apps – SQL, Explorer, the SharePoint Portal, .NET programming, SOAP and Web Services, lately regarded as not the chicest way of creating au fait Web 2.0 apps.

Anyway, bottom line, he says ominously, “Microsoft owns the data.”

Alfresco means to let a breath of fresh air into that closed room.

Alfresco Labs 3 is basically transparent to the end user, Newton said. Drop the new Alfresco repository in and they don’t know they’re not using SharePoint, and they also reap the advantages of being able to leverage their investments in Linux and Java, as well as .NET, reducing their SharePoint total cost of ownership.

They can, if they want, use something other than a Microsoft operating system, database, application server, development system and portal while making the most of REST and scripting for Web 2.0 projects.

In Newton’s mind, at least, “The massive growth of SharePoint has benefited the enterprise content market (ECM) market, but at the same has created pent-up demand for an open alternative that is compatible with Microsoft.”