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