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