[FRex]

There's also using ARM, Calyos stuff[0]

Some old Macs were also 'potentially' silent if you were to today remove the HDD and the optical drive, which were the only mechanical parts[1].

[0] - https://www.youtube.com/watch?v=9LauL5JxYis

[1] - https://en.wikipedia.org/wiki/Power_Mac_G4_Cube