Titanium is an open source platform for building native mobile, tablet, and desktop applications using JavaScript. It allows developers to write apps once using JavaScript and deploy them to various platforms including Android, iOS, and desktop operating systems without needing to know Java, Objective-C, or other native languages. Some key features include cross-platform capabilities, native performance and user interfaces, and support for mobile and desktop APIs on Android, iOS, and desktop platforms. Titanium uses a declarative programming model where apps are created by combining standard Titanium UI elements and APIs.