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