The document discusses building cross-platform mobile apps. It outlines several architecture options for mobile apps including native apps, web apps, and SMS apps. Native apps have issues with fragmentation, web apps have sandboxing limitations, and SMS apps have discoverability problems. The best approach depends on goals and target market. Web apps are generally the cheapest to produce, most standardized, and easiest to distribute option. Hybrid approaches like PhoneGap combine the benefits of native and web. The document provides an overview of tools like jQTouch and PhoneGap for building mobile web apps and wrapping them as native apps. It also covers considerations for the mobile context and building offline web apps using technologies like Web Storage, Web SQL Database, and Application Cache.