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