Here is the full list of all 58 Horace achievements. It takes around 20-25 hours to unlock all of the achievements on Windows.
Complete all other achievements.
Complete the game.
Reach the end of the game having cleaned one million things.
Save the Man in Black.
Don't save the Man in Black.
Find all the alternate title screen skins.
Win The One Tournament.
Defeat the helicopter boss.
Travel to the secret moon base.
Defeat the Ether boss.
Clean 1000000 things.
Die 1000 times.
Complete the auto map by visiting every room in the mansion.
Find all the secret rooms in the mansion.
Defeat the Fire boss.
Defeat the Water boss.
Defeat the Air boss.
Push all the rubber ducks into the water in the Laundry Room.
Get the high score on all the arcade games.
Find an alternate title screen skin.
Buy all possible shop items..
Get the kids blamed for shop lifting.
Defeat the Earth boss.
Find a secret room in the mansion.
Reunite with Heather and the Old Lady.
Meet up with Alice and Sim.
Read 15 teletext pages.
Go on a most excellent adventure with the Professor.
Run the BASIC program everybody knows and loves...
Catch 200 objects.
Buy an item from a shop.
Earn £10000 from jobs, junk yards and other winnings.
Watch a train arrive and leave at any station.
Help to sort the post.
Kidnap Mr Deck from the TV Studio.
Clean 100000 things.
Play an arcade game.
Score 100 baskets in total.
Take your first train ride.
Earn £1000 from jobs, junk yards and other winnings.
Help to make bricks.
Earn £100 from jobs, junk yards and other winnings.
Help to wash dishes.
Spring Logan from prison.
Learn to play the drums.
Empty 10 bins.
Defeat the Nanobot Boss.
Defeat the K-Bot 100 Boss.
Use the Atlas Gloves to tidy up the village hall.
Of dead Old Men?
Return the blind man's cat.
Clean 10000 things.
Rescue the family from the burning house.
Venture out of the mansion.
Climb walls with the Shoees for the first time.
Clean 1000 things.
Clean up your first thing.
Completed basic robot training.