- (BOOL) isAppLaunched: (NSString *) appIdentifier {
   NSArray *apps = [[NSWorkspace sharedWorkspace] launchedApplications];
   for (NSDictionary *appInfo in apps) {
      NSString *appId = [appInfo objectForKey: @"NSApplicationBundleIdentifier"];
      if ([appId isEqualTo: appIdentifier]) {
         return YES;
      }
   }
   return NO;
}
 
if ( [self isAppLaunched: @"com.apple.iCal"] ) {
   NSLog(@"iCal est lancé !");
}