List of free research stuff for developerππ½
If you're looking for all programming tools around research (not just free). Check this page List of research Programming Tools

Squeaky
Understand exactly how customers are using your website or web app, without invading their privacy.
Tag: ux, analytics, privacy, research, user-research, ux-testing, ui-testing
1000 recordings per month Unlimited team members Unlimited page views Unlimited analytics history Unlimited heatmaps Unlimited customer feedback responses

Wappalyzer
Find out the technology stack of any website. Create lists of websites and contacts by the technologies they use.
Tag: profiling, information, research
1 User 50 credits/mo

whatruns
Discover what runs a website, a free browser extension that helps you identify technologies used on any website at the click of a button.
Tag: profiling, information, research

Similarweb
Similarweb is the ultimate competitive digital intelligence tool for a complete 360-degree view of your industry, competitors, and customers.
Tag: profiling, information, research
1 user Limited access to historical data
Bonsai | Web Browser
Web-browser for research that helps programmers think clearly.
Tag: browser, research

OA.mg(Open Access for Everyone)
Search for papers or authors, download and read 200 million open access research papers
Tag: search-engine, research

BuiltWith
Web technology information profiler tool. Find out what a website is built with.
Tag: profiling, information, research