Knytt is a freeware game developed by Nifflas in which you play a young Knytt called Knytt possibly from the land of Knytt (located on the planet Knytt?) who is abducted for reasons unknown. On their little trip they bump into an asteroid and crash land on an unknown planet. Despite being the guest it's your task to go get the missing parts of the ship.
The game encourages exploration and is mostly about atmosphere rather than action (there are barely any enemies at all and only a few spiky spikes.)
Knytt stories works in a similar manner but with more powers (run faster, double jump and holograms to name but a few) and is more focused on telling stories (as the name would suggest) and even comes with a level editor so you can make your own games. There is a set of official levels which you should grab as well as the third part pack. I also recommend Don't Eat the Mushroom and Gaia(1.5) which can be found here. These levels normally have different difficulties, multiple endings, no real linear path and very frequently a lot more enemies.
The games come in a .zip so you'll need 7zip or winrar (both a are free) to get them on your comp but that's easy enough.
These games only appear to work on Windows but I'm sure any Mac or Linux or whatever users can work something out.
Let's Play Knytt & Kytt stories by Deceased Crab and others. Watch some nerds play some of the games and give commentary. Some of them use evil naughty words so if you are offended by that... Also, being the nature of Let's Plays there are tons of spoilers if you can call them that. Try the levels before hand if you decide to watch these.
Within a Deep Forest is the game that bought Nifflas a bunch of attention.