I use Week Calendar on my iPhone and iPad, Calendar in OS X, and Outlook at work. The best you can find is separate applications (albeit maybe from one developer and designed to work as companion apps) that share data seemlessly somehow, but none will be without glitches at times - just the nature of anything that tries to syncronize multiple devices frequently over the internet. You could look throught the APp store for something you like for the iOS devices, then check the developer's site to see if they also make something equivalent or near so for desktop and laptop computers. Apps that are written for the iPhone and iPad have optimizations specific to those platforms, while computer programs will be at least slightly different as they will have optimized features specific to them. You will not find a single identical application for all.
