Microsoft today attempted to exorcize the interoperability bogeymen that have haunted it since it was first discovered to be using secret APIs 20 years ago, bogeymen that now quote European antitrust law at it and carry writs from the Court of First Instance in Luxembourg.

To avoid further confrontation with the European Commission, which opened a broad investigation of Microsoft’s interoperability last month, the company said it would voluntarily open up all the APIs and communications protocols in its biggest revenue producers now and forever.

To be clear, it said that these are the APIs and protocols “used by other Microsoft products.”

The decision applies to Vista, Windows Server 2008, SQL Server 2008, Office 2007, Exchange Server 2007, Office SharePoint Server 2007, the .NET Framework and future versions of these “high-volume” products, it said.

Microsoft also promised to document for free the notorious extensions that impact interoperability that it creates when it uses industry standards. It said it would license any patents that cover these extensions on reasonable and non-discriminatory terms at “low royalty rates.”

It did not define “low.”

Microsoft also accommodated the anti-Microsoft OpenDocument Format (ODF) that’s promising to create an endless row with the EC.

It said it would design new APIs for the Word, Excel and PowerPoint programs in its Office 2007 suite so that third parties could plug in non-Microsoft file formats and use them as defaults when saving documents.

It didn’t say when these new APIs would be ready.

Microsoft did say it would try to work more closely with the open source community by creating both an online Document Interoperability Initiative and a more broad-based Interoperability Forum.

The regulators at the EC reacted immediately to the concessions Microsoft outlined in a press release before it staged a conference call this morning.

• Excuse Me, Did Microsoft Just Give the EC the Finger?