Windows: keyrate - keyboard repeat rate configuration utility.

keyrate.cmd

@setlocal enabledelayedexpansion & set "ARGS=%*" & powershell -nop -ex Bypass -c "Add-Type (gc '%~dpf0'|select -Skip 1|Out-String); exit [Program]::Main();" & exit /b !ERRORLEVEL!

// How can I increase the key repeat rate beyond the OS's limit?	
// https://stackoverflow.com/a/11056655

using System;
using System.Linq;
using System.Runtime.InteropServices;

public static class Program {
    [DllImport("shell32.dll")]
    private static extern IntPtr CommandLineToArgvW(
        [MarshalAs(UnmanagedType.LPWStr)] string lpCmdLine, out int pNumArgs);

    [DllImport("kernel32.dll")]
    private static extern IntPtr LocalFree(IntPtr hMem);

    private static string[] GetArgs() {
        string argStr = Environment.GetEnvironmentVariable("ARGS");
        if (string.IsNullOrEmpty(argStr)) {
            return new string[0];
        }

        int nArgs;
        IntPtr argIntPtrs = CommandLineToArgvW(argStr, out nArgs);
        if (argIntPtrs == IntPtr.Zero) {
            return new string[0];
        }

        try {
            var args = new string[nArgs];
            for (int i = 0; i < nArgs; i++) {
                IntPtr p = Marshal.ReadIntPtr(argIntPtrs, i * IntPtr.Size);
                args[i] = Marshal.PtrToStringUni(p);
            }
            return args;
        }
        finally
        {
            LocalFree(argIntPtrs);
        }
    }

    public static int Main() {
        return KeyRate.Main(GetArgs());
    }
}

public static class KeyRate {
    [DllImport("user32.dll", SetLastError = false)]
    internal static extern bool SystemParametersInfo(uint uiAction, uint uiParam, ref FILTERKEYS pvParam, uint fWinIni);

    [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Auto)]
    internal struct FILTERKEYS {
        public uint cbSize;
        public uint dwFlags;
        public uint iWaitMSec;
        public uint iDelayMSec;
        public uint iRepeatMSec;
        public uint iBounceMSec;
    }

    private const uint  SPI_SETFILTERKEYS   = 0x0033;
    private const uint  FKF_FILTERKEYSON    = 0x0001;
    private const uint  FKF_AVAILABLE       = 0x0002;

    private static void Usage() {
        Console.WriteLine("Usage: keyrate <delay ms> <repeat ms>");
    }

    public static int Main(string[] args) {
        if(args.Length != 0 && args.Length != 2) {
            Usage();
            Console.WriteLine("Invoke with no parameters to disable keyrate acceleration.");
            return 1; // exit code => !ERRORLEVEL!
        }

        FILTERKEYS fk;
        fk.cbSize       = 0;
        fk.dwFlags      = 0;
        fk.iWaitMSec    = 0;
        fk.iDelayMSec   = 0;
        fk.iRepeatMSec  = 0;
        fk.iBounceMSec  = 0;

        if(args.Length == 2) {
            fk.iDelayMSec   = (uint) Math.Max(0, Convert.ToInt32(args[0]));
            fk.iRepeatMSec  = (uint) Math.Max(0, Convert.ToInt32(args[1]));
            fk.dwFlags = FKF_FILTERKEYSON | FKF_AVAILABLE;
            Console.WriteLine("Setting keyrate: delay={0}ms, rate={1}ms"
                              , fk.iDelayMSec, fk.iRepeatMSec);
        } else {
            Usage();
            Console.WriteLine("No parameters given: disabling.");
        }

        fk.cbSize = (uint) Marshal.SizeOf(fk);
        if(! SystemParametersInfo(SPI_SETFILTERKEYS, 0, ref fk, 0)) {
            Console.WriteLine("System call failed.\nUnable to set keyrate.");
            return 1; // exit code => !ERRORLEVEL!
        }
        return 0; // exit code => !ERRORLEVEL!
    }
}

Looks good, nice work!