ClosedXML is a .NET library for reading, manipulating and writing Excel 2007+ (.xlsx, .xlsm) files. It aims to provide an intuitive and user-friendly interface to dealing with the underlying OpenXML API.
Html2OpenXml is a small .Net library that convert simple or advanced HTML to plain OpenXml components. This program has started in 2009, initially to convert user's comments from SharePoint to Word.
Fast and easy to use cross-platform .NET library that creates or modifies Microsoft Word (DocX) and later also Excel (XLSX) files without installing any software. Library is based on Open XML SDK
OpenSpreadsheet provides an easy-to-use wrapper around the OpenXML spreadsheet SAX API. It specializes in efficiently reading and writing between strongly typed collections and worksheets.