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mutillidae
OWASP Mutillidae II is a free, open-source, deliberately vulnerable web application providing a target for web-security training. This is an easy-to-use web hacking environment designed for labs, security enthusiasts, classrooms, CTF, and vulnerability assessment tool targets.
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InfluxDB
Power Real-Time Data Analytics at Scale. Get real-time insights from all types of time series data with InfluxDB. Ingest, query, and analyze billions of data points in real-time with unbounded cardinality.
The WAHH contains a pretty solid baseline for understanding web vulnerabilities, but the latest version is from 2011 so it's missing a decade of new techniques. It's not a terrible place to start since a lot of the fundamentals haven't changed in a while, but you'll definitely want to look into things like (as mentioned in another comment) the Web Security Academy as a next step. Other fun options are the OWASP Juice Shop and Mutillidae applications.