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