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