TREPL is described as 'The main goal of this website is to provide a simple to use tool that will enable users to easily discover how computer programs work under the hood.. User can write his own programs and see how the computer's memory changes during it's execution' and is an website in the Development category. There are four alternatives to TREPL, not only websites but also apps for Linux, Mac, Raspberry Pi and Windows. The best alternative is Scratch, which is both free and Open Source. Other great sites and apps similar to TREPL are Code.org (Free), EduBlocks (Free, Open Source) and CodeHS (Paid).
Code.org is a non-profit whose goal is to expose all students to computer programming. We believe that computer programming is a liberal art; it's something EVERY student in the world should be exposed to at some point in their childhood education.