OpenSignal - Mobile analytics and insights on wireless connectivity from Opensignal, the independent global standard for understanding the true state of the world's mobile network.
TotalHotspots - Total Hotspots helps you find your ideal hotspots.
OpenCellID - OpenCelliD is the largest Open Database of Cell Towers & their locations. You can geolocate IoT & Mobile devices without GPS, explore Mobile Operator coverage and more!
Instabridge - Crowdsourced free wifi (now on Android)
CellID Finder - Find a cell phone location using LAC/CellID, GSM BTS coordinates
Wifi Locations - A community driven map for free or not free wifi locations.