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