One of the main appeals of Android for many enthusiasts (or anyone looking to install emulators) is that you can easily sideload applications not available from the Play Store. Things are very different over in the Apple world, but that could change soon, as the United States Supreme Court has ruled that consumers can sue Apple for its App Store monopoly.
If you're completely unfamiliar with iOS, the only avenue for distributing apps on the platform is through Apple's own App Store, through which the company takes a 30% cut on all purchases. The low market share of iPhones compared to Android devices has largely shielded the company from antitrust fines and lawsuits, like those Google has been receiving lately, but complaints about iOS being a "walled garden" have been present since the first iPhone launched in 2007.
A group of iPhone owners has accused Apple of violating US antitrust rules, and today the Supreme Court ruled that the group is within its legal right to sue the company. Apple previously claimed that it was just an intermediary for purchases, but the Supreme Court ruled otherwise.
The ruling doesn't mean that the group will win any lawsuit against Apple, only that the group can sue Apple. Perhaps in the not-too-distant-future, you'll be able to sideload apps on iPhones just as easily as you can on Android devices.