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
Sleep with another player (group sleep)
Cut down 1000 trees
Play through entire game without killing or eating animals. Alone in Single Player or together in Multiplayer.
Pass 50,000 steps
Share a weapon in MP
Cut down 100 trees
Share a food or drink item in MP
Revive 10 co-op players
Revive one co-op player
Finish Game
Kill all animal types and display heads
Eat an entire family
Chop up 50 bodies
Eat all mushroom types
Build a super long wall
Catch fish with a trap. Alone in Single Player or together in Multiplayer.
Find all missing passengers
Kill shark. Alone in Single Player or together in Multiplayer.
Explore all caves
Grow all plant types
Collect all cassette tapes!
Craft all items
Knock down 6 or more trees with 1 explosive. Alone in Single Player or together in Multiplayer.
Sleep on yacht
Killed downed enemy with rock
Eat an enemy
Make and wear stealth armour
Repair a shelter
Craft 10 medicine items
Set off 20 bombs
Kill bird with arrow
Collect all robot pieces
Kill 6 or more fish with a stick of dynamite. Alone in Single Player or together in Multiplayer.
In Single Player, kill 100 cannibals
Use the compass
Kill a bunny. Alone in Single Player or together in Multiplayer.
Survive 5 nights
Survive 1 night