(from November 2019 and for testing the transmission of Nmea 0183 sentences the tool Nmea0183Tester is better)
This tool has the name Nmea4Wifi and can be used it to setup the Nmea4Wifi multiplexer. However it is a powerful tool to test Nmea 0183 sentences reception and transmission. If you forget the commands related to interaction with the Nmea4Wifi multiplexer, you can use it with any other multiplexer. You can test a variety of situations. Just one example - you can send a file containing Nmea sentences to the Nmea2Wifi or to the Nmea4Wifi multiplexer using the UDP protocol and set the multiplexer to send back the received sentences by wifi using TCP. Then you can set the tool to record in a file the sentences received by TCP. Finally you can compare the initial sent file with the received recorded file to see if there was any error or loss. In the future I may post a video tutorial about this tool.
You can download the tool below. You should download the file Nmea4Wifi.zip and extract it to an empty folder. Then you execute the file Nmea4Wifi.exe. This file was released in January of 2019. In November 2019, I made a small improvement contained in the file Nmea4Wifi_R1.zip. This new archive only contains the executable Nmea4Wifi.exe which should replace the old one. There is a "What is New" menu that explain the changes.