At the time Codeacademy came out, there was not another product quite like it. As a programming teacher in secondary school for the last 10 years, I can say that I’ve tried many different products and websites. The closest I could find to this is www.w3schools.com which as an online editor where you can try out some code snippets in realtime. Codeacademy goes one step further and has set / planned tutorials to over this. The timing of CodeAcademy follows advances in web programming technology that would allow a side like Codeacademy to exist. Also note that around the same time, we saw the debut of similar web-based applications like Google Docs (which came in a few years earlier).
My only criticism of Codeacademy is that its lessons are a little too directed. I used them in my class for the last two years, but I decided not to use them this year. Learning to code is not a straight ahead process. As you learn, you take many detours from the singular path onto other side routes. To use an analogy, you can’t effectively learn to code by following programming book chapter by chapter. That will lead you to learn to program the examples that have in their app / book.