It is Google's e-learning platform that provides courses and labs (step-by-step trainings in Google Cloud). Before cloudskillboost it was called Qwiklabs which

It is Google's e-learning platform that provides courses and labs (step-by-step trainings in Google Cloud). Before cloudskillboost it was called Qwiklabs which was acquired by Google a couple of years ago. It is completely legit and has a OAuth login flow using your Google Identity. For Google partners the trainings are free. (Source: working at a Google Cloud partner)