Edit: I have converted the firmware that I created before to just output the SPS tagged SSIDs, RSSI and channel as comma separated values instead, as the ESP module doesn't have decent math libraries, doesn't do floating point arithmetic very well and is quite slow to update:

https://github.com/subpos/esp_wifi_scanner

You can use this firmware to do trilateration on another embedded platform. Plus you can possibly use multiple ESP receivers to do multiple scans at once (I will alter this firmware to scan on a GPIO active high shortly so you can trigger a scan).

I am in the process of creating a basic ESP8266 based SubPos receiver (like a GPS receiver module).

An ESP8266 module with the SubPos receiver firmware, will generate NMEA messages based on the currently visible nodes and calculate a position. This position could be used for indoor drones or the like. The ESP module returns a scan once every 2 second or so, so this module might be a little slow for some applications. You could increase this speed by limiting to a single channel to scan.