RingZer0 Team's online CTF offers you tons of challenges designed to test and improve your hacking skills through hacking challenge

website: http://ringzer0team.com/

challenges: http://ringzer0team.com/challenges

Every folders represent various kind of challenges.

Binaries (Windows / Linux) (0 / 28)
Coding challenges (0 / 17)
Cryptography (0 / 16)
Forensics (0 / 22)
Jail Escaping (0 / 3)
JavaScript (1 / 7)
Pwnage Linux (0 / 14)
Shellcoding (0 / 7)
SQL Injection (0 / 24)
Steganography (0 / 13)
SysAdmin Linux (0 / 8)
Web (0 / 29)