Fing Network Tools
Fantastic tool for network administrators. It shows you all devices, connected to a network including their IP-adresses. So, it's easy to connect serveral devices.
Great tool to check your screen for defects. It displays serveral colors, you can switch by tapping your screen. So, you easily can see, if your screen is faulty or has faulty pixels.
Shows you surrounding Wifi-Networks and it's signal strength. You also could use it as some kind of Geiger (of course only for Wifi, not radio activities). This is useful, when you want to pitch the area, where you have sufficient reception.
WiFi Connection Manager
Good, when you have problems with your Wifi. You can choose, when your phone connects to a better network. It also displays all your networks and has some tools for Ping, LAN scan, Whois and pretty more things. It also shows you the WLAN-spectrum. But for this, I recommend WiFi Analyzer.