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
Craft all items
Explore all caves
Kill all animal types and display heads
Cut down 1000 trees
Find all missing passengers
Play through entire game without killing or eating animals. Alone in Single Player or together in Multiplayer.
Grow all plant types
Eat all mushroom types
Build a super long wall
Collect all robot pieces
Finish Game
In Single Player, kill 100 cannibals
Eat an entire family
Set off 20 bombs
Collect all cassette tapes!
Kill shark. Alone in Single Player or together in Multiplayer.
Craft 10 medicine items
Cut down 100 trees
Revive 10 co-op players
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.
Killed downed enemy with rock
Repair a shelter
Kill 6 or more fish with a stick of dynamite. Alone in Single Player or together in Multiplayer.
Eat an enemy
Survive 5 nights
Chop up 50 bodies
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.
Use the compass
Sleep with another player (group sleep)
Revive one co-op player
Share a food or drink item in MP
Share a weapon in MP
Kill bird with arrow
Sleep on yacht
Make and wear stealth armour
Survive 1 night