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