slack.csx

using SlackAPI;

var client = new SlackSocketClient("[SLACK_TOKEN]");
client.Connect((connected) =>{}, () =>{
    Console.WriteLine("Connected");
    client.PostMessage(
        resp => {
            Console.WriteLine("Posted");
        },
        "[CHANNEL]",
        "Hello Slack from scriptcs"
    );
});
Console.ReadLine();

Before running this, do "scriptcs install slackapi". Replace [SLACK_TOKEN] with your API token and replace [channel] with the channel you want to post to.