Capslator

using System;
using System.Runtime.InteropServices;
using System.Diagnostics;
using swf = System.Windows.Forms;

namespace Capslator
{
    class Program
    {
        static IntPtr _hookID = IntPtr.Zero;
        static HookProc _proc = HookCallback;
        const int WM_INPUTLANGCHANGEREQUEST = 0x050;
        const int INPUTLANGCHANGE_FORWARD = 0x0002;
        const int WM_KEYDOWN = 0x0100;
        const int WH_KEYBOARD_LL = 0x000D;

        static void Main(string[] args)
        {
            _hookID = SetHook(HookCallback);
            swf::Application.Run();
            UnhookWindowsHookEx(_hookID);
        }

        private static IntPtr SetHook(HookProc proc)
        {
            using (Process curProcess = Process.GetCurrentProcess())
            using (ProcessModule curModule = curProcess.MainModule)
            {
                return SetWindowsHookEx(WH_KEYBOARD_LL, proc, GetModuleHandle(curModule.ModuleName), 0);
            }
        }

        private static IntPtr HookCallback(int nCode, IntPtr wParam, IntPtr lParam)
        {
            if (nCode >= 0 && wParam == (IntPtr)WM_KEYDOWN)
            {
                if (swf::Keys.CapsLock == (swf::Keys)Marshal.ReadInt32(lParam))
                {
                    PostMessage(GetForegroundWindow(), WM_INPUTLANGCHANGEREQUEST, INPUTLANGCHANGE_FORWARD, 0);
                    return (IntPtr)1;
                }
            }
            return CallNextHookEx(_hookID, nCode, wParam, lParam);
        }

        [DllImport("user32.dll")]
        public static extern IntPtr GetForegroundWindow();

        [DllImport("user32.dll", CharSet = CharSet.Auto)]
        public static extern bool PostMessage(IntPtr hWnd, int Msg, int wParam, int lParam);

        [DllImport("user32.dll", SetLastError = true)]
        public static extern IntPtr SetWindowsHookEx(int hookType, HookProc lpfn, IntPtr hMod, uint dwThreadId);

        [DllImport("user32.dll")]
        public static extern IntPtr CallNextHookEx(IntPtr hhk, int nCode, IntPtr wParam, IntPtr lParam);

        [DllImport("user32.dll", SetLastError = true)]
        [return: MarshalAs(UnmanagedType.Bool)]
        public static extern bool UnhookWindowsHookEx(IntPtr hhk);

        [DllImport("kernel32.dll", CharSet = CharSet.Auto)]
        public static extern IntPtr GetModuleHandle(string lpModuleName);

        public delegate IntPtr HookProc(int code, IntPtr wParam, IntPtr lParam);
    }
}