Here is the full list of all 11 Osmos achievements. It takes around 6-8 hours to unlock all of the achievements on Windows.
Complete five levels in any Forever zone.
Complete three levels in each Sentient Forever zone.
Complete all Force zones.
Complete the game.
Complete all Sentient zones.
Collapse the system in level F2-3 by feeding the Attractor.
Unlock all zones.
Complete all Ambient zones.
Complete all tutorial zones.
Complete three levels in each Ambient Forever zone.
Complete three levels in each Force Forever zone.