KeyboardKit is an open-source library that can be used to build your own keyboard apps.
You can use KeyboardKit to build keyboard apps for iPhone and iPad, using technologies like Swift, SwiftUI and UIKit. It supports keyboards that mimic the native keyboards, with alphabetic, numeric and symbolic inputs, emojis etc. as well as entirely custom views.
Checkout the GitHub repository for more information about features and how to add KeyboardKit to your own projects.
KeyboardKit is completely open-source, which means that you can contribute to the project by sending PRs with new features, bug fixes etc.