The Unity Engine has been used as the back-end on some fairly high-profile games across consoles and mobile devices. If you're an aspiring developer or hobbyist and curious to get your own hands on it, the iOS and Android versions are now free for a limited time.
The Unity Store lists both versions as free through April 8, also known this year as Easter Sunday. After that date the price will rise again, though the "Pro" versions are still currently going for $1,500 a pop. That's probably slightly out of most hobbyist price ranges, so try out the free versions while you can.