This is part of a short series highlighting some free web based tools that can help teach kids to code.
The courses on Programmr take you through it step-by-step with hands-on coding practice. It also offers coding simulators, so you can write your code and test mobile, databases, Web, and rich media apps right in your browser. It's a very good option for those who have a basic knowledge of different programming languages, but want to develop their skills even further or pick up a new language.
Programmr is free, but (I think?) there are some costs associated with certification. it also has a great section based around community challenges.