Capture the Flag Resources

I recently started playing CTF (Capture the Flag) and here are some of the resources I've found helpful.

Cryptography

Factordb -- database of large factored numbers
How RSA works
HashID
John the Ripper
Large hex/decimal conversion @ ss64.com
OpenSSL
rsatool
yafu
featherduster

Steganography

exiftool
StegSolve
GIMP
ImageMagick
TinEye
Google Image Search
Sonic Visualizer
Magic Eye Viewer (can do this in GIMP too)

Forensics

file
binwalk
foremost
strings
Wireshark
Emacs hexl-mode or vi with xxd as hex editors

Reverse Engineering

GDB
radare2
objdump
strace
ltrace
Uncompyle2
Uncompyle6

Recon

DNS tools: dig, host, etc.
Whois
The Wayback Machine
wget/curl one liners
nmap

Web

Browser developer consoles
Burp Suite
Nikto
Dirbuster
JWT Decoder
sqlmap

Binary Exploitation

pwntools
pattern create Metasploit modules

Misc