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Reverse Engineering:
GDB – http://www.gnu.org/software/gdb/download/
IDA Pro – https://www.hex-rays.com/products/ida/support/download.shtml
Immunity Debugger – http://debugger.immunityinc.com/
OllyDbg – http://www.ollydbg.de/
radare2 – http://www.radare.org/y/?p=download
Hopper – http://www.hopperapp.com/download.html
nm – unix/linux tool
objdump – linux tool
strace – linux tool
ILSpy – http://ilspy.net/
JD-GUI – http://jd.benow.ca/#jd-gui-overview
FFDec – http://www.free-decompiler.com/flash/download.html
dex2jar – http://code.google.com/p/dex2jar/
uncompyle2 – https://github.com/wibiti/uncompyle2
Hex editors:
Windows:
HxD – http://mh-nexus.de/en/hxd/
Neo – http://www.new-hex-editor.com/hex-editor-downloads.html
Linux:
Bless – http://home.gna.org/bless/downloads.html
wxHexEditor – http://www.wxhexeditor.org/download.php
Exe unpackers – Unpacking Kit 2012 – http://forum.exetools.com/showthread.php?t=13610

Networking:
Wireshark, tshark – https://www.wireshark.org/download.html
OpenVPN – https://openvpn.net/
OpenSSL – https://www.openssl.org/related/binaries.html
tcpdump – http://www.tcpdump.org/
netcat – http://netcat.sourceforge.net/
nmap – http://nmap.org/download.html

Steganography:
OpenStego – http://www.openstego.info/
OutGuess – http://www.outguess.org/download.php
Steghide – http://steghide.sourceforge.net/download.php
StegFS – http://sourceforge.net/projects/stegfs/
pngcheck – http://www.libpng.org/pub/png/apps/pngcheck.html
GIMP – http://www.gimp.org/downloads/
Audacity – http://audacity.sourceforge.net/download/
MP3Stego – http://www.petitcolas.net/steganography/mp3stego/
ffmpeg (for video analysis) – https://www.ffmpeg.org/download.html

Forensics:
dd – unix/linux tool
strings – unix/linux tool
scalpel – https://github.com/sleuthkit/scalpel
TrID – http://mark0.net/soft-trid-e.html
binwalk – http://binwalk.org/
foremost – http://foremost.sourceforge.net/
ExifTool – http://www.sno.phy.queensu.ca/~phil/exiftool/
Digital Forensics Framework (DFF) – http://www.digital-forensic.org/download/
Computer Aided INvestigative Environment (CAINE) Linux forensics live distribution – http://www.caine-live.net/
The Sleuth Kit (TSK) – http://www.sleuthkit.org/sleuthkit/download.php
Volatility – http://code.google.com/p/volatility/

Scripting / PPC (Professional Programming and Coding):
Text editors:
Sublime Text – http://www.sublimetext.com/
Notepad++ – http://notepad-plus-plus.org/
vim – http://www.vim.org/
emacs – http://www.gnu.org/software/emacs/

Crypto:
Cryptool – https://www.cryptool.org/
hashpump – https://github.com/bwall/HashPump
Sage – http://www.sagemath.org/
John the Ripper – http://www.openwall.com/john/
xortool – https://github.com/hellman/xortool
Online tools:
http://www.crypo.com/
http://www.cryptool-online.org/
http://rumkin.com/tools/cipher/
Modules for python – pycrypto – https://www.dlitz.net/software/pycrypto/

From http://delimitry.blogspot.in/2014/10/useful-tools-for-ctf.html