N-n-n-nineteen

In a complete change of tone from recent posts, I want to tell you about what I consider to be the perfect puzzle game: Hyperframe. It's challenging enough to make you think, but not so hard that I gave up in frustration. It looks good, it remembers which ones you've solved and which you haven't, and it's free. What more do I need to say to convince you of its worthiness for trial?

You have to link coloured squares on the surface of a cube without crossing any other lines, and there are forty puzzles in all. The early ones are straightforward, to ease you into the way you need to think, then gradually you need to abandon the obvious approaches to solving them. Later on, the size of the cube increases, giving you more and more possibilities to think through. After many days of distraction, I've reached the point now where I've solved all of them except Number 19.

If you know of anything similar, please let me know. Tomorrow I'll tell you about a couple of others I like.