Wouldn't the Netduino 3 Ethernet be simple enough? It looks heavier than the wifi model, because of the Ethernet socket, but I guess the inner logic is simpler. My guess is that it's just useless to keep up three models. Without Ethernet and Wifi, the board would be a Duino, right? Sure the Net refers to .NET, but I guess it's the SD card and the internet routines that benefit the most from the C# and .NET stuff.