ClosedXML makes it easier for developers to create Excel 2007/2010/2013 files. It provides a nice object oriented way to manipulate the files (similar to VBA) without dealing with the hassles of XML Documents. It can be used by any .NET language like C# and Visual Basic (VB).
For more information see the wiki
If you want to include ClosedXML in your project, you can install it directly from NuGet
To install ClosedXML, run the following command in the Package Manager Console
PM> Install-Package ClosedXML
ClosedXML allows you to create Excel 2007/2010/2013 files without the Excel application. The typical example is creating Excel reports on a web server.
If you've ever used the Microsoft Open XML Format SDK you know just how much code you have to write to get the same results as the following 4 lines of code.
var workbook = new XLWorkbook();
var worksheet = workbook.Worksheets.Add("Sample Sheet");
worksheet.Cell("A1").Value = "Hello World!";
workbook.SaveAs("HelloWorld.xlsx");