BrainHQ has a free exercise call Daily Spark. They email you a link to the short exercise each day. It only takes a few minutes. One can just ignore the sales pitch to subscribe by Xing it out at the top right.

It would be interesting to see how people with PCS can do the exercises. The issue is not the level of accomplishment but rather dealing with the way the exercises are presented. Speed, visual, auditory, instructions, etc.

Here is a link:
Brain Exercises, Brain Training, Brain Health – BrainHQ from Posit Science