Sure, you could use a washboard to wash your clothes, but those of us with access to washing machines generally find them a whole lot easier to use. But nothing sounds quite like a washboard, when you play it with a guitar pick or drum brushes. How useful something is often depends on how you define its usefulness.
What do you like to use in some way other than what it was designed for?
Keeping with the musical theme, I primarily play electric bass in a duet with my wife who covers guitar and vocals. Since we are only two people I fill in the electric guitar solos on the bass. This improvisation is unexpected and takes people by surprise the first time they hear us perform.
Placed old dial telephones in a room our grandchildren use for play. They enjoy them and creates a chance to share some family history.
Washboard memory…a wonderful sound and “picture” rubbing wax crayons across washboards of my mother and grandmother. Blessings come so easily…just listen and look.