Here’s the umbrella website for these auto layout libraries using the Cassowary algorithm http://overconstrained.io/

It seems this was Apple’s auto layout, but links to the developer documentation are now broken. My conclusion the last time I looked into this is that it seems Apple has switched to a different approach with their new SwiftUI layout engine.

Edit: this blog post from October discusses the switch from Auto Layout to SwiftUI in some detail https://kean.github.io/post/swiftui-layout-system