Comparing with Wappalyzer and BuiltWith, here's why we think we have something different (and maybe better):
1. WhatRuns detects fonts, Wordpress plugins and themes (tens of thousands of them).
2. Ability to follow sites (and know what techs websites started using/ditched).
3. Very lightweight compared to our counterparts, and arguably better UI ;)
4. More accurate data. BuiltWith can be very inaccurate as you might've already noticed. Wappalyzer is fairly accurate, but limited in technologies. WhatRuns is trying to be the best of both worlds.
The latter is what I've been using and seems to have more users with higher ratings
[1] - https://chrome.google.com/webstore/detail/wappalyzer/gppongm...