cottage industry 
noun
A business or manufacturing activity carried on in people’s homes: weaving was an important cottage industry [mass noun]: conditions in cottage industry were hardly rosy...
- Medicine, which was largely a cottage industry until the Second World War, has been transformed by several factors.
- The considerable increase in business has created a cottage industry in the professions.
- Despite stiff competition, there is a big demand for cheap varieties of detergent powder, which can be manufactured as a cottage industry.