Here is a list of all the ciphers Ciphey plans to support. Pick one and implement it please :) <3
Here's how to incorporate it into Ciphey:
https://github.com/Ciphey/Ciphey/wiki/Adding-your-own-ciphers
Full list of implemented ciphers:
https://github.com/Ciphey/Ciphey/wiki/Supported-Ciphers

Easiest

• First letter of every word, first letter of every line, 2nd letter of every word etc (Add support for Nullcipher-like inputs (i.e. NATO Alphabet) #336)
• T9 phone keypad cipher (like the old Nokia phones) (Add T9 decoder #422)

Ciphers / Encodings

• Playfair cipher (Add Playfair cracker #345)
• Badly implemented RSA
• Monoalphabetic Substitution Cipher (Add monoalphabetic substitution cracker #347)
• Vigenère Autokey Cipher (Add vigenere autokey cracker #348)
• Beaufort Cipher (Add Beaufort Cracker #349)
• Beaufort Autokey Cipher
• Columnar Transposition Cipher (Add Columnar Transposition cracker #350)
• Railfence Cipher (Add Railfence/Zig-Zag cracker #351)
• Double Transposition (Add Double Transposition cracker #352)

Done

• Base8
• Base58 https://github.com/keis/base58 (both Bitcoin & Ripple alphabets)
• Base85
• Base85 ASCII version (Python library for this)
• Base 62 with alphabet 0-9A-Za-z** (Most link shorteners use this alphabet, and it's the default in CyberChef + the online Base62 decoders)
• Vigenere Cipher
• Atbash Cipher
• Base91
• If a text only contains 2 letters X and Y, we may turn it into Binary and see if that works. similarly we could do the same for hex and octal etc
• Minecraft enchanting table (see Add more decryption methods #63 (comment) )
• XOR
• Base69 (Add base69 decoder #335)
• DNA codons (ATCG DNA letters) (Add DNA codons decoder #354)
• Baudot ITA2 (Add Baudot decoder #355)
• SMS Multi-tap (Add SMS Multi-tap decoder #340)
• DTMF frequency (Add DTMF decoder #424)
• A1Z26 (Add A1Z26 decoder #344)
• Prisoner's tap code (Add support for Prisoner's Tap Code #337)
• Brainfuck (Add Brainfuck interpreter #353)
• ROT47 (Add ROT47 cracker #342)
• ASCII shift (Add ASCII shift cracker #343)
• UUencode (Add UUencode decoder #433)
• Affine (Add affine cracker #346)
• Baconian cipher (Add Baconian decoder #432)
• Soundex (Feature request: Soundex #412)
• Braille (Add Braille Decoder #439)