Samorost 1, 2 and Machinarium

Now that most of the exams are over, I feel I can safely link to this excellent little game, Samorost. I think it wins the award for most creative use of lichen, ever.

 
Samorost 1 is pretty short. Samorost 2 is longer, but I think you have to pay money for the full game (which I did, many years ago; it's only $5, says the website).

 The producers, Amanita Design, also made Machinarium, but that's got a bit less of a biological theme. Still fun though, and lots longer. I also bought that one (now $10; no idea what currency).