Jon Jagger has built an excellent web application for practicing test driven development. The environment consists of multiple languages and exercises that are easily accessible via web browser. I really like the concept because it eliminates the need to install any development environments or libraries before you can get started. This would be pretty perfect for demonstrating and training TDD together with a team, since everybody would immediately have the same system setup without any hassle. Cyber-dojo also comes with ability to review how code has changed over time and what the effect those changes have had on the test results. At the top of the screen there’s history of traffic lights and it’s easy to get hooked with that familiar red-green – cycle.