My latest project is a WiFi probe request logger called Sentinel.
A ZeroW with an extra wifi dongle set to monitor mode. When a wifi probe request is recieved, it is filtered by its signal strength, then checked against an exclude list of known devices. If it gets through these filters, it is a potential suspect should a crime be committed. The MAC address is cross referenced to get the vendor I'd.
A MySQL database rcords timestamp, MAC address, Vendor, Signal strength and SSID. This data can be managed via a web interface using HTML and PHP.
If a crime is committed ( it has been designed for an environment where burglary is a problem), the database will list the MAC address of any devices in the area at the time, along with an SSID that the device has connected to. This information will be handed over to the police.