A clock app? Why on earth would you need yet ANOTHER clock app?
Because Horst is not just another highly-configurable clock app that is filled to the brim with bells and whistles.
On the contrary.
Horst is different and very single minded.
Horst is here to help you make the perfect clock picture to correct the erroneous timestamp your ill-configured digital camera wrote into the EXIF data of your pictures.
For that purpose Horst will show you the current date and time - in glorious black-on-white to make it easy to photgraph, and in perfecty large letters so you can still read it even when the image is reduced to the miniscule size of a thumbnail.
Your mission, should you choose to accept it, is to take a picture of Horst with your digital camera, import your photographs from your digital camera into your photo library and use your photo organization software to adjust the EXIF timestamps to perfectly match the beautiful picture that you made of Horst.
You can also use Horst to synchronize the clocks of multiple cameras that you used to shoot a single project. Or vacation. Whatever floats our boat. Just do the above on each camera.
If you are still sitting there asking yourself 'But. WHY?', you are not the target audience. Go download another clock app. Same applies if you are an exclusive smartphone photographer. You don't need Horst. You don't deserve Horst. Time to move on.