Rhodes is a smartphone app framework that allows developers to write apps once using HTML and Ruby and deploy them across multiple platforms like iPhone, Android, and BlackBerry. It uses a client-server architecture with RhoSync to synchronize data even when offline. Rhodes provides generators, libraries, and RhoHub for hosted development and testing without needing to install device SDKs. Version 2.0 updates include native mapping on all devices, a metadata framework, and using Redis to power the faster and lighter RhoSync server.