OWASP Juice Shop
Probably the most modern and sophisticated insecure web application
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The application contains a vast number of hacking challenges of varying difficulty where the user is supposed to exploit the underlying vulnerabilities. The hacking progress is tracked on a score board. Finding this score board is actually one of the (easy) challenges!
Apart from the hacker and awareness training use case, pentesting proxies or security scanners can use Juice Shop as a "guinea pig"-application to check how well their tools cope with JavaScript-heavy application frontends and REST APIs.