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