One such tool, which will become a bedrock of Teach Code this year, is repl.it, a tool with a development team based out of San Francisco. My favorite part about repl.it is that they have managed to create flexible, real-time code environments that do not need to be installed on the computer, but still manage to save student work. Better still, there are 30 instructional programming languages available. Teachers are not tethered to any specific sequences of instruction, so students can work at any pace, on any project or code, and their correct responses will run correctly, even if they do not "match" an auto-grader, as is the case with many current tools. Yet, the code will be marked with an error message, which students can then look up to trouble shoot their issue.
Repl.it has truly created a tool that I am excited to use; I must say straight off that I stumbled upon them by accident and in no way am I being endorsed - their product is just so great that I feel the need to give them space and thanks.
Soon, you will be able to also find the public login for teach code repl.it example lessons available on the site! In the mean time, stop by their website and show them some love. If you already teach a code class, try it out. You'll be impressed.