What is ChessOK?

Other than Steps, ChessOK is the second system I recommend. I discovered the ChessOK in 2006, when I read the book "Rapid Chess Improvement". The book is talking about an adult player, who trains himself to improve from 1321 to 2041 in two years, with the help of the software named "CT*Art". No coach, just repeating and strenuous training. That's sounds interesting. As an adult player, if I could improve without any coach, it's a very attractive proposal. I started the research and found out ChessOK is the publisher of CT*Art. Not only they published the CT*Art, they also published a series of software. It's a great treasure chest. I started to buy their software for me and for my daughter.

We started with Chess Tactics for Beginners, which is geared for students from 300 to 1000. Then we worked on Chess School (no longer available), Chess Tactics for Intermediate Players, and CT*Art. I myself had done the CT*Art for 3 times. I never tried the Seven Circles recommended in the book. In my mind, it's close to insane and very unlikely we could execute it. We also did several other software from ChessOK, mating, endgames, studies, opening lab, and etc. 

Nowadays, all software have their app version. ChessOK (aka ChessKing or ChessQueen) has published more than 40 chess apps. They are also offered as subscription: https://learn.chessking.com/learning/purchases/subscriptions-info

You can find the full list at ChessOK.com or ChessKing.com. There are apps for every level, from beginners (mate in 1) to expert players (2400). If you are interested, you could read the following article about how to train an IM with ChessOK software: https://chessok.com/?p=21207

I didn't improve 700 in 2 years, but I went from 1326 to 2034 in 11 years.