Here is the full list of all 45 The Forest achievements. It takes around 50-60 hours to unlock all of the achievements on Windows.
In Single Player, don't kill any cannibals for more than 10 days in a row
Build a super long wall
Revive 10 co-op players
Play through entire game without killing or eating animals. Alone in Single Player or together in Multiplayer.
Finish Game
Eat all mushroom types
Catch fish with a trap. Alone in Single Player or together in Multiplayer.
Pass 50,000 steps
Find all missing passengers
Cut down 1000 trees
Kill all animal types and display heads
Craft 10 medicine items
Share a weapon in MP
Set off 20 bombs
Explore all caves
Collect all robot pieces
Craft all items
Eat an entire family
Kill shark. Alone in Single Player or together in Multiplayer.
Collect all cassette tapes!
Revive one co-op player
Kill 6 or more fish with a stick of dynamite. Alone in Single Player or together in Multiplayer.
Sleep on yacht
Use the compass
Eat an enemy
Grow all plant types
Repair a shelter
Killed downed enemy with rock
Chop up 50 bodies
In Single Player, kill 100 cannibals
Knock down 6 or more trees with 1 explosive. Alone in Single Player or together in Multiplayer.
Share a food or drink item in MP
Kill bird with arrow
Cut down 100 trees
Make and wear stealth armour
Survive 5 nights
Kill a bunny. Alone in Single Player or together in Multiplayer.
Survive 1 night
Sleep with another player (group sleep)