I have 3 exercises on this website:
The chess visualization exercise is very good for chess and non-chess players. It improves your visualization and that can be very helpful in many cases!
The 2th exercise is the Mental Calculation Training, this is inspired by how Nikola Tesla exercised. If you use this exercise a lot you will develop an intuitive sense of mathematics.
The last of them is the Think About This-exercise, this mental exercise will improve your thinking in philosophy and in politics. You will be training the process of really thinking about something, so you can think through more dilemmas in your life and in ethical dilemmas. Deep thinking is one of the hardest things you can do and only a few has truly mastered it, but that should not discourage you in any way to keep on the deep thinking!