I had used the brain app Elevate on and off prior to my sabbatical. I vowed to make a habit of doing it every day since I no longer had work to engage the mind,. I also picked up a second app, Lumosity, mentioned by one of my friends. I have done these, almost without fail, since December of 2019.
Elevate has four different categories: math, speaking, writing, and reading. Basically your standardized test. The free version has a decent variety of games, keeps track of your stats, and compares your results to previous (although not in a very transparent way as difficulty increases). I like it as the modules, 3 per day, are consistently less than 2 minutes each. I frequently do them between sets in my strength training.
Lumosity on the other hand is more variable in duration. You get 3 per day, the same as Elevate, but some modules can take closer to 10 minutes, and others only a minute or so. The categories are speed, memory, attention, flexibility, & problem solving with a healthy dose of math on the side. As these categories indicate, they work different parts of the mind, and some that are desperately needed given smart phones dominance in our life. (Mainly that we lack attention as a culture and don’t have to remember anything.)
They both have merits at the end of the day. If I had to pick one, it would likely be Lumosity. It annoys me more, which means it likely challenges me more as well.