From http://stackoverflow.com/questions/11072804/mac-os-x-10-8-replacement-for-gestalt-for-testing-os-version-at-runtime

NSAppKitVersionNumberExample.c

NSInteger osxVersion;
if (floor(NSAppKitVersionNumber) <= NSAppKitVersionNumber10_6) {
    //10.6.x or earlier systems
    osxVersion = 106;
    NSLog(@"Mac OSX Snow Leopard");
} else if (floor(NSAppKitVersionNumber) <= NSAppKitVersionNumber10_7) {
    /* On a 10.7.x or earlier system */
    osxVersion = 107;
    NSLog(@"Mac OSX Lion");
} else if (floor(NSAppKitVersionNumber) <= NSAppKitVersionNumber10_8) {
    /* On a 10.8 - 10.8.x system */
    osxVersion = 108;
    NSLog(@"Mac OSX Moutain Lion");
} else {
    /* 10.9 or later system */
    osxVersion = 109;
    NSLog(@"Mac OSX: Mavericks or Later");
}