Kayleth is a 1986 science-fiction text adventure published for the Commodore 64 by the British company Adventuresoft UK. It was written by Stefan Ufnowski, the author of Rebel Planet, and it is a classic of its kind: every location comes as a prose description topped with a static illustration, and you act by typing English commands.

The backdrop is grim. The planet Zyron and its peaceful people have been enslaved by the tyrant Kayleth, who works them to exhaustion mining a rare mineral called Chromazin. You are one of the enslaved Zyroneans, and the plan is simple and insane in equal measure — bring the tyrant down yourself.
It plays the way parser adventures always played: you explore, examine everything in sight (EXAMINE is your best friend), hoard objects and puzzle out which of them unpicks which obstacle. The tone is dark, machine-filled science fiction with no fairy-tale relief, and the game will kill you without hesitation for a careless step — save often and draw a map, because without one you will be lost inside ten minutes.
A fair warning: without decent English, Kayleth is unplayable, and some puzzles have the era's stubborn streak of demanding one exact wording. Genre fans, though, get an atmospheric, well-crafted piece from an experienced author; for everyone else it is a fascinating lesson in what gaming imagination looked like when most of the picture lived in the player's head.
It runs on oldgame.cz straight in the browser — keep a pen and paper handy.