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