Here is the full list of all 21 Last Day of June achievements. It takes around 3-4 hours to unlock all of the achievements on Windows.
See the epilogue.
Accepted the truth.
Prevent the crash caused by June.
Deliver the gift.
Prevent the crash caused by the Hunter.
Collect every memory of the Hunter.
Knock over four vases.
Prevent the crash caused by the Best Friend.
Prevent the crash caused by the Kid.
Peek at Carl and June at the Lake
Wake Up.
Try to involve Teddy in the surprise.
Give June a flower.
Pick every petal of a single flower.
Open the gate to the Graveyard.
Look at every viewable in Carl and June's house.
Listened to every diorama.
Shoot the ball at the basketball hoop four times.
Collect every memory of the Kid.
Collect every memory of the Best Friend.
Collect every memory of the Old Man.