Is there something I can use to control Arduinos easily over Ethernet with .NET?
I don't use .net but I have done this using php website to control a door lock over ethernet.

My solution was to use the ethernet to recieve commands and be able to use them on the arduino through http calls. And when it was done send a http call back to the server with some data. I was doing a door lock program for example. Please ignore anything talking about doors, locking, unlocking, or other requirements to certain calls, I am just providing examples about how it COULD be used, not that you need to include my door lock code in your project to get it to work.

As far as how that works out with .net that's up to you, however I can give you a hand getting your messages back and forth.

first you want to create the ethernet connection to your router. put this in your header section.

#include &lt;UIPEthernet.h&gt;
// assign a MAC address for the ethernet controller.
// fill in your address here:
byte mac[] = {
  0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xED
};

// fill in an available IP address on your network here,
// for manual configuration:
IPAddress ip(127, 0, 0, 1);

// initialize the library instance:
EthernetClient client;

char server[] = "www.example.com";
//IPAddress server(127,0,0,1);  // numeric IP for www.example.com (no DNS)

int waitTime = 3L;

unsigned long lastConnectionTime = 0;             // last time you connected to the server, in milliseconds
const unsigned long postingInterval = waitTime * 1000L; // delay between updates, in milliseconds
// the "L" is needed to use long type numbers


throw this in your main loop so it doesn't constantly make http requests spamming a server.

// if ten seconds have passed since your last connection,
// then connect again and send data:
if (millis() - lastConnectionTime &gt; postingInterval || buttonState == 0) {
  httpRequest();
}


Create a method to handle httpRequest because shoving everything under the main is kinda sloppy.

Alright so there will be quite a bit here because http headers are kinda lengthy.

// this method makes a HTTP connection to the server:
void httpRequest() {
  // close any connection before send a new request.
  // This will free the socket on the WiFi shield
  client.stop();
  // if there's a successful connection:
  if (client.connect(server, 80)) {
    Serial.println("connecting...");
    // send the HTTP PUT request:
  Serial.println("String is " + readString);
  if(readString == "Ready" || readString == ""){  
    client.println("GET /command.txt HTTP/1.1");
    where = "web";
    waitTime = 5L;
  }
  else{
    // here is the basic format of sending a get command
    //this specific request is so that I can tell where the command came from. I had a web client / mobile app that could control the door AND you could also control it from a physical buttom. The door would have to reply either way to the web server (READ: .net application) in order to have the correct status always show up on the web end.

    client.print("GET /update.php?where=Arduino&amp;command=Ready&amp;status=");
    if(readString == "Reset"){
      client.print("Reset");
    }
    else if(isLocked){
      client.print("Locked");
    }
    else{
      client.print("Unlocked");
    }
    client.println(" HTTP/1.1");
    waitTime = 1L;
  }
  client.println("Host: www.example.com");
  client.println("User-Agent: arduino-ethernet");
  client.println("Connection: close");
  client.println();

    // note the time that the connection was made:
    lastConnectionTime = millis();
  }
  else {
    // if you couldn't make a connection:
    Serial.println("connection failed");
  }
}


TL;DR if you wanna use ethernet you need to use all of ethernet.
Start by creating your connection to the router statically (watch for conflicts).

Then create a method of watching for incoming data or waiting for a command if there isn't one. (server call).

Then create A FULL HTTP REQUEST in order to pass your request through. Shorting any parts of this last part and you will either end up with bad request errors or will simply fail.

Let me know if you need anything else or if this was useful to you!