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