A Good Place to Start.
Decoders
CacheSleuth – Geocaching Tools & Cipher Solvers
dCode – Online Ciphers, Solvers, Decoders, Calculators
GeocachingToolbox.com – All geocaching tools a geocacher needs
Boxentriq – Online Tools for Ciphers, CTFs and Code-breaking
Images tools
StegOnline
Image Steganography
Code Image Decoder – CacheSleuth
Audio
Audio Spectrogram Analyzer | Boxentriq
Strange and Unusual
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