I'm quite a fan of those brain-training games that you often see advertised in magazines and on the TV. If you are too, here's one for your PC which is free to download and use. It's called N-Back, and you can get it from http://brainworkshop.sourceforge.net. It runs on all recent versions of Windows, and the download is 10 MB.
The object of the game is simple, but playing it isn't so easy! Each game lasts around a minute. During this time, every 3 seconds or so, a blue square flashes up on the board for a short time (see illustration below) and, though your PC speakers, you'll hear a nice lady read out a random letter of the alphabet from A to Z.
All you have to do is as follows. If the position of the blue square is the same as it was last time, ie a few seconds ago, press the "A" key to indicate a position match. Alternatively, if the letter dictated by the nice lady is the same as last time, that signifies an audio match so press the "L" key instead. That's all there is to it.
The game is called N-Back because the key to playing it is to remember what happened in the past, ie 1, 2 or 3 events back. When you first start the game, N is set to 2, meaning that you actually need to remember what happened 2 events ago. If you're new to the game, you'll find this impossible, so start by changing N to 1. The web site contains full instructions on how to do this.
Apparently, minds cleverer than mine reckon that you can improve your short-term memory by playing this game for around 20 minutes, 4 or 5 times a week. A pretty good result for a free app, so long as you remember to keep playing!
My thanks to Keith Harvey for alerting me to this fascinating Hot Find.