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