LiveCode is both an open-source and proprietary cross-platform rapid application development language.
Pro GUI-driven development
In LiveCode, you start by dropping GUI elements into place, then add the code that makes them function. This lets beginners see visual results right away, which is often more exciting (especially for young students). It also lets you focus on the user interaction before you get into the nitty-gritty of code implementation.
Pro Highest ROI compared to other popular cross-platform development tools
Fluid production - from prototyping to delivery in one toolkit. With a high-level language that includes GUI controls as native elements, code more directly expresses the end-user experience. And the platform coverage is awesome, nearly unmatched.