Alternate post title: Conumdra. For this is a short semi-text adventure from Tom Jubert, who's best known for writing the Penumbra series of heavily bephysicsed action-puzzlers. Apparently ir/rational began life as minigame for inclusion in one of the Penumbras, but now find itself standalone.
It is a free videogame.
Therefore you will play it.
It tests your logic and deductive reasoning.
Therefore you may be too lazy to play it.
But you should.
It won't take long (though I got stuck for a long time on the last of its 10 puzzles, but that's because I'm not a real human being), it'll make you feel slightly clever, and it might make you question some of its logic. I know I felt a couple of solutions didn't ring true. But then that's probably part of the point.
I don't wish to describe it in much detail because I fear that going into its mechanics might make it sound boring - instead, I'll summarise that it concerns a stalemate between a (presumed) human and a sinister machine which holds him/her/it captive. You have to break that stalemate. Using only THE POWER OF YOUR MIND. Um, and your mouse.
Also: it's well-written, funny, and takes an unexpected and vicious pop at an Austrialian politician. You'll like it.