ctrl-f1.c

/*
 * ctrl-f1
 * -------
 * Query or toggle the "Full Keyboard Access" hotkey, Ctrl-F1
 *
 * make CC=clang CFLAGS="-framework Carbon" ctrl-f1
 */

#include <Carbon/Carbon.h>

/* Undocumented Goodness extracted from CGSHotKeys.h */
typedef enum {
	kCGSHotKeyToggleFullKeyboardAccess = 12,
	kCGSHotKeyFocusMenubar = 7,
	kCGSHotKeyFocusDock = 8,
	kCGSHotKeyFocusNextGlobalWindow = 9,
	kCGSHotKeyFocusToolbar = 10,
	kCGSHotKeyFocusFloatingWindow = 11,
	kCGSHotKeyFocusApplicationWindow = 27,
	kCGSHotKeyFocusNextControl = 13,
	kCGSHotKeyFocusDrawer = 51,
	kCGSHotKeyFocusStatusItems = 57,

	kCGSHotKeyScreenshot = 28,
	kCGSHotKeyScreenshotToClipboard = 29,
	kCGSHotKeyScreenshotRegion = 30,
	kCGSHotKeyScreenshotRegionToClipboard = 31,

	kCGSHotKeyToggleZoom = 15,
	kCGSHotKeyZoomOut = 19,
	kCGSHotKeyZoomIn = 17,
	kCGSHotKeyZoomToggleSmoothing = 23,
	kCGSHotKeyIncreaseContrast = 25,
	kCGSHotKeyDecreaseContrast = 26,
	kCGSHotKeyInvertScreen = 21,
	kCGSHotKeyDecreaseDisplayBrightness = 53,
	kCGSHotKeyIncreaseDisplayBrightness = 54,
	kCGSHotKeyToggleVoiceOver = 59,

	kCGSHotKeyExposeAllWindows = 32,
	kCGSHotKeyExposeAllWindowsSlow = 34,
	kCGSHotKeyExposeApplicationWindows = 33,
	kCGSHotKeyExposeApplicationWindowsSlow = 35,
	kCGSHotKeyExposeDesktop = 36,
	kCGSHotKeyExposeDesktopsSlow = 37,
	kCGSHotKeyDashboard = 62,
	kCGSHotKeyDashboardSlow = 63,

	kCGSHotKeySpaces = 75,
	kCGSHotKeySpacesSlow = 76,
	kCGSHotKeySpaceLeft = 79,
	kCGSHotKeySpaceLeftSlow = 80,
	kCGSHotKeySpaceRight = 81,
	kCGSHotKeySpaceRightSlow = 82,
	kCGSHotKeySpaceDown = 83,
	kCGSHotKeySpaceDownSlow = 84,
	kCGSHotKeySpaceUp = 85,
	kCGSHotKeySpaceUpSlow = 86,

	kCGSHotKeyToggleCharacterPallette = 50,
	kCGSHotKeySelectPreviousInputSource = 60,
	kCGSHotKeySelectNextInputSource = 61,

	kCGSHotKeySpotlightSearchField = 64,
	kCGSHotKeySpotlightWindow = 65,

	kCGSHotKeyToggleDockAutohide = 52,
	kCGSHotKeyToggleFrontRow = 73,
	kCGSHotKeyLookUpWordInDictionary = 70,
	kCGSHotKeyHelp = 98,
} CGSSymbolicHotKey;

extern bool CGSIsSymbolicHotKeyEnabled(CGSSymbolicHotKey hotKey);
extern CGError CGSSetSymbolicHotKeyEnabled(CGSSymbolicHotKey hotKey, bool isEnabled);

void get(void) {
	printf("Full Keyboard Access is: %s\n", CGSIsSymbolicHotKeyEnabled(kCGSHotKeyToggleFullKeyboardAccess) ? "enabled" : "disabled");
}

void set(const bool enabled) {
	CGSSetSymbolicHotKeyEnabled(kCGSHotKeyToggleFullKeyboardAccess, enabled);
	get();
}

void usage(char *const self) {
	printf("Usage: %s [-q|-t|-f]\n", self);
}

int main(int argc, char *const argv[]) {
	int opt;
	while ((opt = getopt(argc, argv, "qtf")) != -1) {
		switch (opt) {
		case 'q':
			get();
			break;
		case 't':
			set(TRUE);
			break;
		case 'f':
			set(FALSE);
			break;
		default:
			usage(argv[0]);
			return -1;
		}
	}
	if (argc == 1) {
		get();
		usage(argv[0]);
	}
	return 0;
}

Thanks to karstenBriksoft for the tip!
http://twitter.com/_karsten_/statuses/17152088894