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