This app was mentioned in 8 comments, with an average of 1.38 upvotes
The only thing I know of that is actually proven to make you "smarter" is training your working memory by using n-back tasks.
https://play.google.com/store/apps/details?id=phuc.entertainment.dualnback
Search for Dual N-Back in the Play store. I've used this one, and it has a free and $2.99 version. https://play.google.com/store/apps/details?id=phuc.entertainment.dualnback
There's definitely more free ones that are well rated. N-Back training has been shown in studies to improve memory. Good luck!
http://brainworkshop.sourceforge.net/
I mainly do it on the phone using this app https://play.google.com/store/apps/details?id=phuc.entertainment.dualnback
For Android Brain N-Back: https://play.google.com/store/apps/details?id=phuc.entertainment.dualnback&hl=en
Decent options, allows for 4 stimuli: Position, sound, color, image.
https://play.google.com/store/apps/details?id=phuc.entertainment.dualnback&hl=en
The only brain training game that actually works
You can set the sounds to piano keys instead of letters