Pgyuri's All-Key-Tester is a well presented bit of software designed to show which keys on your ZX Spectrum are responding and which ones are not.
On an emulated machine the only real fun to be gleaned from this entry is testing your knowledge of which key combinations will map correctly to the special keys on the original Speccy 16/48K rubber-keyed model, however, I'm told that when utilized on a real Spectrum that the real excitement begins.
Unfortunately mine hasn't worked in 20 years.
Apparently there's also a bit of hardware that goes with this - The All-Key-Presser - but I couldn't tell you a thing about it as, save a couple of tantalising .jpeg photos, it looks like ours got lost in the post?
I'd also love to tell you how Pgyuri's software works, however, he's implemented some kind of security mechanism into the supposedly BASIC program that I was unable to crack.
With so little to go on I'm going to leave this review there but, if you're interested, here's what one of the more popular Speccy mags had to say about it: