Here is the full list of all 20 GNOG achievements. It takes around 1-2 hours to unlock all of the achievements on Windows.
Finish the game
Complete HOM-3
Leave no trace
Unlock every level
Complete CANDY
Watch what you eat
Complete LAB-O
Daydream at the blackboard
Complete LOG
Leave no worm behind
Complete VORT-X
Test the astronaut for space sickness
Complete SUB-01
Complete EATER
Keep the kitchen clean
Complete PURP-L
Discover what lurks below
Please don't bother the amphibians
Experiment in the studio
Complete FRG-Y