On-line utility to convert Excel files to CSV

On-line application that reads an Excel file and returns the first sheet in it in CSV format with each item separated by a specified separator (',' by default).

You can also call this conversion utility from the command line.
For example, using curl to process an Excel file "file.xls" and save the results to "file.csv", separated by semi-colons:

curl -F "f=@file.xls" -F "separator=;" https://jansson.net/apps/excel_to_csv/ -o file.csv