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