One useful trick is that you can rely on the headless version of LibreOffice to do the conversion, here on Mac for instance (but also work on Ubuntu with a slightly different call):

    /Applications/LibreOffice.app/Contents/MacOS/soffice --headless --convert-to xlsx file.csv

Note, though, that some conversion errors can still occur (I've seen one personally a long time back).

This works for many other formats, too: anything to PDF, for example.

A resource hog, though - had to close it off into its own container, lest it gobble up all available RAM.

For Python, there's XlsxWriter[0] (creation of new excel files) and OpenPyXL[1] (creation of new and manipulation of existing files).

[0]: http://xlsxwriter.readthedocs.io/ https://pypi.python.org/pypi/XlsxWriter

[1]: https://openpyxl.readthedocs.io/ https://pypi.python.org/pypi/openpyxl

For anyone using Ruby I'd recommend the (open-source) axlsx gem, I've had great results being able to treat Excel generation like I'm rendering a view.

I've had luck with that one too for the times I actually need a real Excel file.

For Java there are at least two good solutions: https://poi.apache.org/ and https://github.com/plutext/docx4j/ (or JExcelAPI)

+1 for Apache POI; we actually used that at Google for exporting XLS reports for ads.

tablib[0] is one option for Python. There are quite a few libraries that handle export. Excel files (and other Office) file formats are just zip files containing XML. For a while now, this has been an open standard[1].

[0] https://github.com/kennethreitz/tablib

[1] https://en.wikipedia.org/wiki/Office_Open_XML

I've found the Python pyexcel library to be the most flexible option to read/write Excel files. https://pypi.python.org/pypi/pyexcel/0.0.9

Curious if you've tried tablib. I haven't used either, but knowing kenneth_reitz tablib is quality :)

I've used openpyxl a lot for these kinds of tasks, and found it really useful.

One nice feature with openpyxl is that it can work together with excel template files. So I can create a template in excel with whatever looks and features I want and then use openpyxl to populate those templates with data.

HTML table in a file with a .xls extension.

One of my favorite old tricks. Works with renaming a .csv to .xls.

Newer versions of Excel will warn the user of possible file corruption if they try to open an .html file that has been renamed to .xls. The file can still be opened but the warning is bothersome.

An alternative is to make a .xlsx file with Excel, then unzip it. You'll get a folder with text files and then you'll see how to generate your own.

PHPExcel for, you guessed it, PHP. An order of magnitude less hassle than CSV ("the files you generate are wrong, but only on some computers! Fixitfixitfixit!!!"), and surprisingly powerful.

Note: Last time we used it for large data report generation results were slow and consumed huge amount of memory.

Depends on the amount of data, calculations, and formatting. For "output this array of arrays as XLSX instead of CSV", I find its current performance acceptable.

Most reasonably popular languages will have platform-independent open source read-write libraries for Excel. I've used the Python version of this with minimal pain.

Create it as a report in SSRS, then they can export to XLSX, PDF, CSV, etc

I've used this a couple of times: http://papaparse.com/