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