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