LibreOffice running natively in the browser via WebAssembly
Note that it will download around ~300Mb of data directly to your browser, so it might take a bit to load from slow connections.<p>Here's the related video from FOSDEM: 
<a href="https://fosdem.org/2022/schedule/event/lotech_lowa/" rel="nofollow">https://fosdem.org/2022/schedule/event/lotech_lowa/</a>