The best alternatives to Webapplizer are WhatRuns, SimilarTech, and BuiltWith. If these 3 options don't work for you, we've listed a few more alternatives below.
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WhatRuns is a free technology lookup tool for developers, designers and salespeople to discover the technologies used on any website. Available for free on Chrome and Firefox. Featured 3 years ago.
BuiltWith is an Internet services company based in Manly, Australia, which launched in August, 2007. The goal of BuiltWith is to help web developers, researchers, and designers track what technologies are being used by other websites, which may help them to decide what technologies to implement themselves.
My Codeless Website is a website scanner that detects themes, page builders, plugins, and tracking tools. It's a super simple tool to get a quick summary of any website.