PHPExcel
Library offering classes to read from and write to spreadsheet formats
...Developers can create complex spreadsheets with styled cells, formulas, charts, images, and multiple sheets programmatically. It also supports reading existing files, iterating through cells, applying data validation, and converting between formats. Because it handles the details of Excel file structures—including relationships, themes, and various metadata—users don’t need to manage proprietary file internals themselves. The API allows for cell access using row/column indexes or column letters, batch updates, and streaming writes to reduce memory usage. ...