From Healthcare Administration Degree:

Stay on top of your game mentally and slow the effects of aging on your brain by keeping it in excellent shape. It’s easy to do and costs little to no money with all the resources available on the Internet. The following tools, exercises, and games will stimulate your brain and give it the exercise it needs to stay in top form.

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Online Brain Games

The online games listed here are designed specially for working out your brain.

1. Strategy Games. These seven games will require you use strategy, which is an excellent way to exercise your brain.
2. HAPPYneuron. Try the fun games and activities here to build your brain fitness. Join for a fee to have access to fitness programs and personal coaches.
3. Braingle. Some of the fun brain activities here include brain teasers, riddles, trivia, and brain exercises.
4. Sharp Brains Brain Teasers and Games. Give these 50 games designed just for exercising your brain a try.
5. Games for the Brain. Your brain will get a boost with games like Mastermind, chess, and Sudoku here.
6. BrainCurls. Try your hand at jigsaw puzzles, memory games, and games that sharpen your observation skills.
7. Brain Bashers. Find plenty of video games at this site that are meant to sharpen your mental prowess.
8. Fit Brains. These games are designed by scientists to develop your brain power.
9. BrainTraining 101. Logic, puzzle, memory, classic, and action games are the focus of this website’s brain games.

Read the rest of the list here.