If you need a free Windows spreadsheet that can cope with very large spreadsheets, these are the best choices:
1. LibreOffice Calc (recommended by ChatGPT but I had difficulties installing it in my Windows 10 machine).
Completely free and open source.
Handles very large files better than many free alternatives.
Good compatibility with Excel (.xlsx).
Suitable for datasets with hundreds of thousands of rows, limited mainly by your PC’s RAM.
2. OnlyOffice Desktop Editors
Free desktop suite.
Excellent compatibility with Excel files.
Modern interface.
3. Apache OpenOffice Calc
Free, but development is much slower than LibreOffice.
Generally not my first recommendation.
If your spreadsheets contain millions of rows or are primarily for data analysis rather than traditional spreadsheets, you may be better off using:
DuckDB (free, extremely fast for huge datasets)
SQLite (free, lightweight)
Given your radio astronomy work, if you’re logging large amounts of SDR or interferometry data, I’d recommend LibreOffice Calc for ordinary analysis and DuckDB once your data grows beyond what a spreadsheet handles comfortably.
If LibreOffice Calc won’t install, there are several other free Windows GUI options:
OnlyOffice Desktop Editors – Probably the best alternative. Modern interface, free, and very good Excel compatibility.
WPS Office – Free version available with a spreadsheet component. It includes some ads and optional premium features.
Apache OpenOffice Calc – Older but still usable.
Gnumeric – Lightweight and free. Less feature-rich, but handles many spreadsheet tasks well.
If your goal is to work with very large CSV files (millions of rows), a spreadsheet may not be the best tool. A free GUI such as DB Browser for SQLite can often handle much larger datasets after importing them into SQLite.