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