"Suveh Nux" is a short, puzzle-oriented piece of interactive fiction by David Fisher, with a neat premise: the player is trapped in a vault (that's not the neat part) and can escape only if he learns the magical language that controls his environment.
Plenty of interactive fiction games involve puzzles about magic words. "Suveh Nux" takes this a step further: there's a whole magical grammar to learn, including verbs, nouns, and modifying phrases. The challenge isn't just to learn new magic words, but to learn to string the words together into short spells. The result is a set of well-integrated challenges that encourage lateral thinking. And the game rewards experimentation: even spells that serve no practical purpose produce often amusing results.
The puzzles in "Suveh Nux" aren't too hard, but in case you get stuck, there is also a built-in hint system and instructions for play.
The links above point to JIG's internally developed Flash-based Z-Machine interpreter (thanks asterick!), with the story files hosted here by kind permission of the game's author, David Fisher. That means you can now play these games in your browser rather than having to download and run the game in a standalone interpreter.
If you would rather download the game, you can get the game file from ibiblio.org. If you do choose to download the game, you will need an IF player to play the game file. If you don't have one installed, try Gargoyle (Windows) (mirror) or Zoom (Unix or Macintosh). (Zoom for Macintosh also allows you to browse and download additional IF games right from within the player, a neat feature for future use.) Another option is Splatterlight available for Macintosh and Unix.
If you enjoy "Suveh Nux", I also recommend "Words of Power", by Stark Springs: it too uses an additive magic-word grammar, though the puzzles are less tightly integrated and the game as a whole is more sprawling.