Does anybody know a tool like https://fast.com or https://speedtest.net that can be deployed inside an intranet. I know about various benchmarking tools like iperf, but I'd like to have something that can be run by regular users from a browser.
Since you didn't mention it has be free, Speedtest actually provides exactly what you want: https://www.ookla.com/speedtest-custom
For a free very basic (only time based) solution, https://www.raditha.com/blog/archives/1791.html offered a small PHP test, assuming your Intranet allows PHP. But they didn't make it possible to run directly, so I modified to do so. Can you try it? If it doesn't work like you want, you can post it on https://stackoverflow.com to ask for further development (if you do, please link here to the question there):
<?php $s="0"; for($i = 0 ; $i < 16; $i++) $s .= $s; $date_start = time(); for($i = 0 ; $i < 2048; $i++) echo $s . nl2br("\n"); $date_end = time(); echo nl2br('Started at ' . date('r', $date_start) . ' Ended at ' . date('r', $date_end) . ' Took ' . date_diff(new DateTime("@$date_start"), new DateTime("@$date_end"))->format('%hh %im %ss')); ?>