Bluntly, I don't play games much on my computer. I do play Bridge on the computer and on the Internet, but that's more of a calling than wasting time.
Like everybody else, I DO find myself with a couple of minutes to kill. And that's when I click on the Summing icon. Summing is a game, available at Raphael Fetzer's site. Now, the site is in German, but there's an English link on the right-hand side. You can probably figure out how to download the game fairly easily.
And playing the game can take all of a minute. Sometimes two or three. That's all. Perfect for waiting on hold, when focusing in on the jerk who put you on hold would be enough to drive you crazy.
What is Summing? It's an arithmetic game. You have a board filled to within one row all round of random single-digit numbers. In fact, it's actually only the digits 0-8. On the left, you have a stack of buttons with the same digits. As the one comes to the top, you have to place it on the board. If you place the piece on the board in such a way that ALL the pieces touching it add up to it (or it plus ten, or it plus 20), the pieces and the one you placed all disappear. The goal is to make all the pieces disappear. I've cleared the 9x9 board with the 64 starting pieces in as few as 15 moves. I can do most boards in the low 20's and I average a shade under 20, I would guess. There are times when I get an unlucky run and the game can last five minutes and 60 moves, but those are the exception to the rule.
What's great about Summing is its brevity. It's easy to learn and to master. And it doesn't hurt to keep your arithmetic skills in daily use. Oh, and it distracts from that gawdawful elevator music while you are waiting on hold.