Egmont shared on facebook recently that Circular+ was free. It looks like it still is, and I highly recommend it.
Not only can you create tiny planets with Circular+, but you can choose to repeat the image, which allows you to customize your planet.
Inverting the tiny planet effect is also very cool, as you can see below in the image of the building.
What sets this app apart from other planet apps is the ability to add some effects from brainfevermedia’s other apps. There are flares, planets, birds (dear god, why??,) and even some creative centers that you can place on your planet, like I did in the first example.
Planet with a Gas Giant center
Same shot, inverted with a sun disc center.
Add 1 repeat
Add 3 repeats
Get the app here.