Appcelerator Tititanium is… A free and open source application development platform that lets you create native mobile, tablet and desktop application experiences using existing web skills.
Truly native applications
Titanium translates the code into native application code. The application code is written in JavaScript and being interpreted during runtime. See more: The Titanium Architecture
JavaScript
Code is written in JavaScript, using functions that the Titanium API exposes. Apart from using it to access special device features (such as the camera), it also enables the developer to render native UI elements (such as tables, buttons, native maps etc.).
Introduction
Advantages
Compared to similar technologies, Titanium has the advantage of a native application performance.
Use any IDE of choice to develop Titanium applications.
Decreased software development time.
The amount of skilled web developers in the world makes it a strong developer base.
Open Source – It is Free (except for Titanium+ Starter modules, Paypal, Barcode reader, etc..) http://www.appcelerator.com/products/plans-pricing/