- hackerone.com
- picoctf
- MIT Mystery Hunt:MIT Mystery Hunt: https://puzzles.mit.edu/
- CTFLearn https://ctflearn.com
- ctfcyber.org small, basic challenges (sponsored by cyber.org)
- PortSwigger Academy
- Overthewire:https://overthewire.org/wargames/
- Code Quest Academy: https://lmcodequestacademy.com
- Hack the Box Hack the Box
- https://www.vulnhub.com/
- https://ctftime.org/
- capturetheflag.withgoogle.com
- https://cmdchallenge.com practice commandline basics
- tryhackme.com: tried this because they have the advent of code. but the learning paths are very theoretical and not practical.