Useful tools
Is my cache on Crown Land?
Check the Nova Scotia Crown Land interactive map
Do my caches need maintenance?
To search for your caches with DNFs or other issues, go to this link at project-gc. Log in with your geocaching ID, and then select your username under "Profile name".
The geocaching website also has a cache owner dashboard.
Puzzle tools:
Geocaching Toolbox: https://www.geocachingtoolbox.com/
CacheSleuth: https://www.cachesleuth.com/ (wide variety of tools; their "helpful links" page points to over 70 other geocaching sites including many puzzle tools)
DCODE: https://www.dcode.fr/en
including columnar transposition cipher
Geocaching puzzle help facebook group (closed) https://www.facebook.com/groups/geocachingpuzzlehelp/ . The group includes an extensive list of helpful sites (too long to list here).
Images:
http://fotoforensics.com/ (analyse images)
https://incoherency.co.uk/image-steganography/ (online tool to hide images inside the lower "bits" of other images, or extract them)
https://pinetools.com/c-images/ (various image manipulation tools including edge detection and edge enhancement)
https://ezgif.com/maker (can split an animated gif into frames)
http://magiceye.ecksdee.co.uk/ (Magic Eye viewer)
https://tineye.com/ (reverse image search)
Google search by image: https://www.google.com/imghp?hl=en
Cipher tools at rumkin.com
Text Manipulator at rumkin.com
https://www.wolframalpha.com/ (online mathematical tool)
https://quipqiup.com/ (automatic cryptogram solver)
http://altamatic.com/crypt (another automatic cryptography solver)
https://www.jsingler.de/apps/logikloeser/index.php?language=en (logic puzzle solving tool)
Coordinates and maps:
Free GPS maps for Garmin: http://garmin.openstreetmap.nl/
GPS converter: http://boulter.com/gps/ (at http://boulter.com/geocaching/ )
GPS visualizer: http://www.gpsvisualizer.com/
OpenStreetMap: https://www.openstreetmap.org
Databases, lists, finding and organizing caches, cachers, etc:
Geocaching Swiss Army Knife (GSAK): https://gsak.net/
Project-GC: https://project-gc.com/
Trip planning / safety:
AdventureSmart Trip Planning tool from https://www.adventuresmart.ca/ . App available from Apple App Store, Google Play, or online at URL.
Log sheets: