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