Xamarin is a popular tool for building cross-platform mobile apps that allows developers to share up to 80% of code across platforms. It uses C# and provides access to native APIs and libraries. Some benefits include simplified development, faster coding through code reuse, and access to portable class libraries and components. However, Xamarin also has some drawbacks like high licensing costs, delays in supporting latest platform versions, and limited community support and documentation. The document also discusses how Xamarin was used to build an automated asset management app with RFID scanning capabilities that achieved 85% code reuse across platforms.