Here is the full list of all 20 Alone achievements.
Finished the game
Finished the game in Extreme mode
Hunted down a Bear
Froze to death
Built a level 3 base camp
Maxed out cooking skills
Well this was a great idea...
Found a Canister
Why not?
Found a Bow
Survived the first 10 days
Ignited the campfire
Yay!
Finished the game in under 50 days
Turned on a generator
Fell in to the lake
So close to death
Finished the game in under 50 days in Extreme mode