CircuitLab is coming up on its one year anniversary, and the startup (now part of Y Combinator’s winter 2013 cohort) now boasts 70,000 monthly active users, who run an average of one circuit simulation every six seconds. The phenomenal traction for the electrical-engineering-focused startup has a lot to do with the team offering up a tool that’s both free and particularly well-suited to educational use, and it bodes well for CircuitLab’s chances of helping early stage hardware startups get off the ground.