Type in Dvorak on a QWERTY-configured Windows.

d2q.c

/*
 * cc d2q.c -o d2q.exe -Wl,-subsystem,windows
 */

#include <windows.h>

int mapping;

int remap(int o){
	return
		o == 'Q'? 222 :
		o == 'W'? 188 :
		o == 'E'? 190 :
		o == 219? 191 :
		o == 221? 187 :
		o == 188? 'W' :
		o == 190? 'V' :
		o == 191? 'Z' :
		o == 186? 'S' :
		o == 222? 189 :
		o == 189? 219 :
		o == 187? 221 :
		o >= 'A' && o <= 'Z'? "AXJE\xbeUIDCHTNMBRL\xdePOYGK\xbcQF\xba"[o - 'A'] : 0;
}

LRESULT CALLBACK keyhook(int nCode, WPARAM wParam, LPARAM lParam){
	int k;

	if(!mapping && nCode == HC_ACTION && (wParam == WM_KEYDOWN || wParam == WM_KEYUP) && (k = remap(((PKBDLLHOOKSTRUCT)lParam)->vkCode))){
		mapping = 1;
		keybd_event(k, ((PKBDLLHOOKSTRUCT)lParam)->scanCode, wParam == WM_KEYUP? KEYEVENTF_KEYUP : 0, 0);
		mapping = 0;
		return 1;
	}
	return CallNextHookEx(NULL, nCode, wParam, lParam);
}

int WINAPI WinMain(HINSTANCE hinst, HINSTANCE hprevinst, PTSTR lpcmd, int show){
	HHOOK keyhookex;

	keyhookex = SetWindowsHookEx(WH_KEYBOARD_LL, keyhook, hinst, 0);
	MessageBox(NULL, TEXT("Remapping, OK to stop"), TEXT("d2q"), MB_OK);
	UnhookWindowsHookEx(keyhookex);
	return 0;
}

d2q.exe