Khan academy is an educational organisation which is set to educate others in a free courses through their web site and app this is absolutely free of cost this is help ful to many students whether they are children or adults they can refer many things and also complete many courses through onliine and get a certificate too .so if we are busy at our life but to many things to learn is an intrest and so we can fullfill our dreams of working and learning many things and also become a proffesional with a certificate.i recommend this website to be very usefull to every one