iOS has a bunch of basic apps that many people throw into a folder and forget (come iOS 10, however, you'll be able to delete most of them). Many of these apps haven't changed much since they were first added to iOS, and most are very basic in terms of the functionality they offer.
What follows are heavy-duty, professional-level, third-party replacements for a dozen of the most popular apps built into iOS. Many of them are free, but some of the higher-end apps either need to be purchased or use in-app purchases to unlock features.
Most are available for both the iPhone and iPad, and many come with an Apple Watch app too.
If you have a favorite app that hasn't been included here, then feel free to leave a comment below, or send me a message via Twitter.