https://ketohour.com/

Ketohour.com However it is important to vary exercises so that they don't become rote. Of course brain exercises don't have to be exercises in the strictest terms, any activity that involves thinking is an exercise in itself. An activity which involves learning something new is good for the brain, even a simple task being done for the first time engages the brain into thinking mode. Problem solving is a form of brain exercise, especially complex problems with multiple solutions. 

https://ketohour.com/