Three20

three20 is a historically significant iOS framework originally extracted from Facebook’s app, providing a broad set of utilities and UI components for early iPhone development. It introduced a URL-based navigation system, image/caching pipelines, styled text labels, and a photo browser that many apps adopted before iOS shipped similar features. The library championed modularity with packages you could include piecemeal, helping teams standardize networking, model objects, and table view stylings. Because it predated ARC and many modern APIs, it also taught best practices for memory management and asynchronous image loading in its era. Over time Apple’s SDK absorbed or superseded much of its functionality, and the project was archived, but its ideas influenced subsequent open-source libraries. three20 remains an instructive snapshot of how early large-scale iOS apps were structured.