Smartwatches are very much in their infancy right now and Apple's Watch seems to be trying to start it's own trend when it comes to the smartwatch UI. Only thing is that now someone thought it'd be good idea to take that UI and slap it on a large screened device such as the iPhone.
A developer has come up with his own Apple Watch UI for jailbroken iPhone's. It's of course only an experiment and probably not something you'd want to use on a daily basis but it looks fun regardless.
The tweak is not available in the Cydia Store at the moment. To install it on your device, please visit the developer’s Reddit thread and follow the instructions.