It's a free 3D browser game that works even on modern mobile browsers and touchscreen devices running Android and iOS. You do need 3D capable video card though and one of not too old browsers supporting WebGL, but those are all browsers released since 2012 or so and if you really want to play this game it will force you to update your browser, so it's a win win situation, you improve your memory while have one of latest browsers that will make sure you experience web and browser games in the best way possible.
Game tests your memory skills more than anything else, it also trains your brain improving memory skills. You need to match 3 blocks with the same face by turning them. Now this may sound simple, but it's not. You need to keep on matching triplets of block until you've achieved assigned quota for the level before the level runs out. "To Go" on the right side panel is letting you know how many matches you still need to go before completing the level. With each new level game adds a new block face making entire game harder. You will eventually fail to match anything in time.
Flip, memorize, match 3 blocks with the same face, try to complete the level before time runs out. There's also a 24/7 online hiscore table so you can compete with your friends and other players. You can play as a guest, by default, but you can also register a unique hiscore name that will be shared across all my future game.
You can play it here, for free of course: Codergames.com
Here's a short video of gameplay:
I highly recomment one of the browsers in this order: FireFox, Chrome, Safari, Opera, Edge.