Here is the full list of all 51 Summer in Mara achievements. It takes around 20-25 hours to unlock all of the achievements on Windows.
Craft 60 objects.
Unlock the mine.
The sea is dangerous, next time get back to your boat before getting tired.
Read all the messages on Puni Cave.
Complete all the quests from Mûn.
Sell objects for a total of 2000 coins.
Craft 40 objects.
Cook 30 dishes.
Sell objects for a total of 1000 coins.
Cook 15 dishes.
Craft 20 objects.
Meet Saimi.
Collect 90 objects.
Remember...
Collect 60 objects.
Wake up after the tutorial.
Collect 30 objects.
Carry 99 oranges in the backpack.
Complete all the quests from Akaji.
Complete all the quests from Aquila.
Complete all the quests from Awan.
Complete all the quests from Brram.
Complete all the quests from Blu.
Complete all the quests from Litio.
Complete all the quests from Mayo.
Complete all the quests from Pilly, Milly & Tilly.
Complete all the quests from Ecco.
Complete all the quests from Taima.
Complete all the quests from Rigatta.
Complete all the quests from Onzo.
Complete all the quests from Taka.
Complete all the quests from Noho.
Complete all the quests from Napopo.
Cook 50 dishes.
Use the recycle bin 100 times.
Sell objects for a total of 3000 coins.
Get all the Koa's outfits.
Get all the Koa's backpacks.
Build all the main structures on Home Island.
Unlock all the crops on Home Island.
Catch one fish of every type.
Get one farm animal of each type for your island.
Visit all the islands from Mara.
Meet Dunna.
Beat Ereti in a race.
Recover all the chrystalis from the Door.
Defeat the Elit.
Pay the mortgage on your boat.
Sing the old Navy song on its base.
Get the boat to max level.
Ask Caleb to take you back to Qälis.