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