Here are some useful links I've gathered in my time. Hope you'll make a good use of them.
Geocaching & Mapping
project-gc.com -- a really good stats generator, all the stats are free, some tools require modest fee
ruian.poloha.net -- a nice OSM-backed map with trails marked with colour (Czech Republic only)
unicam.camea.cz -- bicycle counters statistics for Prague
Ciphers & codes