Multitools:

CyberChef

https://gchq.github.io/CyberChef/

Cryptii

https://cryptii.com/

Cryptii v2

https://v2.cryptii.com/text/select

Xlate

https://paulschou.com/tools/xlate/  (+ custom octal)

dCode

https://www.dcode.fr/ <-- has frequency analysis, brainfuck, alphabet, substitution with alphabet input, polybius square, zodiac killer, pigpen…

GeocachingToolBox

https://www.geocachingtoolbox.com/ 

Rumkin

http://rumkin.com/tools/cipher/

 

Monoalphabetic substitution:

Quipqiup

https://quipqiup.com/

Boxentriq

https://www.boxentriq.com/code-breaking/cryptogram 

Guballa

https://www.guballa.de/substitution-solver  <-- in English, German, Spanish, French, Dutch & Portuguese

 

Polyalphabetic substitution:

Boxentriq

https://www.boxentriq.com/code-breaking/vigenere-cipher <--  auto vigenére with key length limitation

Guballa

https://www.guballa.de/vigenere-solver  <--  auto vigenére & beaufort decoder in English, German, Spanish, French, Dutch & Portuguese

F00l

https://f00l.de/hacking/vigenere.php <-- vigenére key length calculator

 

Audio:

Audio Morse

https://morsecode.world/international/decoder/audio-decoder-adaptive.html

Spectrogram creator

https://nsspot.herokuapp.com/imagetoaudio/

 

Text:

Caesar

http://theblob.org/rot.cgi <--  Caesar for letters & numbers

Cipher ID

https://bionsgadgets.appspot.com/gadget_forms/refscore_extended.html

base64 looking text

https://aesencryption.net/ 

https://www.online-toolz.com/tools/text-encryption-decryption.php 

https://encipher.it/ 

https://pteo.paranoiaworks.mobi/ 

https://www.samltool.com/decode.php

View none-printables

https://www.soscisurvey.de/tools/view-chars.php 

Word completer

https://www.onelook.com/ <-- search ??i???n??e and get CHIMPANZEE for example

Byte shift

https://cyber.meme.tips/xlate/shifts.html <-- View all byte shifts and all constant XOR's

Casing inverter

https://www.browserling.com/tools/text-invert-case 

English language frequencies https://www3.nd.edu/~busiforc/handouts/cryptography/cryptography%20hints.html

Esolangs decoder

https://tio.run/# 

Large number converter

https://www.mobilefish.com/services/big_number/big_number.php <-- Binary, hex, decimal & base64 conversion

Cipher identifier

https://www.boxentriq.com/code-breaking/cipher-identifier

 

Image:

Stegonline

https://stegonline.georgeom.net/image <--  RGB value extraction

AperiSolve

https://aperisolve.fr/ <--  Image analysis, uses Binwalk, Steghide, Outguess, Foremost, Strings, Exiftool & Zteg

Metadata viewer

https://www.metadata2go.com/

RAW pixels viewer

https://rawpixels.net/  

Image forensics

https://29a.ch/photo-forensics/#forensic-magnifier 

Punch Card decoder

http://laighside.com/punchcard.htm

Spectrogram creator

https://nsspot.herokuapp.com/imagetoaudio/

​

Random steg websites:

Futureboy

https://futureboy.us/stegano/decinput.html <--  JPGs only

Mobilefish

https://www.mobilefish.com/services/steganography/steganography.php

Random steg programs:

Steganpeg

https://steganpeg.apponic.com/ <--  JPGs only

Outguess

https://www.rbcafe.com/software/outguess/ <--  JPGs only

Openpuff

https://openpuff.en.lo4d.com/windows

Silenteye

https://sourceforge.net/projects/silenteye/

​

Others:

Youtube video tag extractor

https://online-free-tools.com/en/youtube_video_tags_extract_url 

Link identifier

https://a4x.me/tools/link/ <-- oHg5SJYRHA0 for example

Hex viewer/editor

https://hexed.it/ 

QR code recovery/building

https://merricx.github.io/qrazybox/ 

 

Hash:

Hash identifier

https://hashes.com/en/tools/hash_identifier 

Hash “cracker”

https://crackstation.net/