Ignition runs the CarPlay UI directly on top of SpringBoard without the need for a vehicle. This makes it very useful for anyone who has their iPad mounted in the car.
Notably, while Ignition is meant for iPad, and iPhones "aren't really supported", you can use it with an iPhone 6 Plus if you really want to.
Ignition can be downloaded from the Big Boss Cydia repository. If you want to see the source code, check it out here. If you want to donate, you can do so here.
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