Esperanto in 12 days is described as 'Teaches you the most important 500 words No registration needed: Just click Start mobile-optimized for smartphones not only free of charge, but also free to use in other projects The course consists of 12 lessons, each with a text a grammar'. There are four alternatives to Esperanto in 12 days for Online / Web-based. The best alternative is lernu!, which is free. Other great apps like Esperanto in 12 days are I Kinda Like Languages (Free), esperanto.ca (Free) and Free Esperanto Course (Free).
I kinda like languages is website with free online introductory and basic language courses of different languages of the world. The courses are made by volunteers and the website is targeted for people who want to learn many languages.
The Free Esperanto Course consists of ten lessons with exercises. You study the lessons by yourself, do the exercises and send them to your tutor by email. Your tutor checks your exercises and answers your questions. In the end you will receive a diploma.