Here is the full list of all 20 Master Reboot achievements. It takes around 6-8 hours to unlock all of the achievements on Windows.
Find the alternative ending
Complete the full game
Complete the full game in Welsh
Complete the Final Level in record time
Find all the virus symbols
Find all of the blue ducks
Get the monorail to the Mainframe
Make the right choice in the Library
Get crushed by a bookcase in the Library
Hit all the viruses in the Graveyard Level
Complete the Hospital Level without a torch
Touch the whale on the Beach Zero Level
Find half of the blue ducks
Go down the wrong path in the Fairground Zero Level
Complete the Aeroplane Level without dying
Complete the Street Level without taking a hit
Listen to the radio show in your Soul Village
Complete the planet puzzle in the School Level without checking the answer
Attacked by the virus in the closet
Read the employee handbook