Yes. As you rightly guessed, it's a website created by Bill Gates! After his retirement from Microsoft, Bill Gates thought of sharing with the world, his thoughts and ideas he was working on. And this, as he thought, could be effectively done through a website.
The Gates Notes talks about what Bill Gates is thinking about, what he is learning and other interesting conversations. It is a beautiful site, nicely designed with a lot of information. One of the things that caught my attention is the "Infrequently Asked Questions" section. Here, Bill talks about the Non-Microsoft topics and expresses his views. The best thing I like about this site is that you can mail Bill Gates regarding your queries and he answers. It may also be featured on the website. Never tried it though; but worth a shot.