Quote from Juampi
Hacker Gateway is a modern, open-source site built by a computer scientist and veteran challenger from Argentina. The site is intended for hackers of all skill levels, and spans several challenge categories, including cryptography, steganography and web, with more to be added in the future. The challenges go from pretty easy to very hard, and subtle hints are given when appropriate so that they never feel unfair.
If you want to put your hacking skills to the test, Hacker Gateway is the site for you!
I'd say "Happy Challenging!" to that! (Gizmore makes me.)