ClosedXML makes it easier for developers to create Excel 2007+ files.

ExtremeML adds new power to the OpenXML SDK 2.0, enabling packages to be created and edited via an intuitive object model and freeing developers from the burden of implementing the low-level detail of OpenXML.

A library to convert simple or advanced html to plain OpenXml document.

Images2OpenXML its an application that uses Office 2007 OCR API to convert images generated by scanned documents to OpenXML documents. There's no need of third party applications anymore to convert documents, you can use this tool for free. It was developed with C#.

An OpenXML API for PHP. Generate and read OpenXML documents.