It is not in the same league as Flent, but I really like <a href="https://speed.cloudflare.com" rel="nofollow">https://speed.cloudflare.com</a> as an in-browser internet speed test. It's backed by a very densely deployed CDN, it tests both loaded and unloaded latency, and it reports jitter and draws candlestick plots.
Dave Taht's bufferbloat project could have gotten way more actual non-technical user data had Flent supported Windows. At least fast.com and Waveform's bufferbloat test [1] exist now.<p>[1]: <a href="https://www.waveform.com/tools/bufferbloat" rel="nofollow">https://www.waveform.com/tools/bufferbloat</a>