Any open source / free library for handling Excel (both *.xls and *.xlsx) files? [duplicate]

Question

I know of some open source libraries for handling with Excel files but these are for only *.xls or *.xlsx, for example NPOI is for *.xls, EPPlus and ClosedXML are for *.xlsx. I don't want to use Microsoft Excel Automation because of the performance matter. Could you please suggest me with some open source or free library meeting this purpose (handle with both *.xls and *.xlsx).

Answer 1

How about spreadsheetlight? Is open-source, with an MIT license.