They are the most basic sewing machines. They are either hand-operated or treadle. The mechanical sewing machine was designed to use where electrical power was inaccessible or nonexistent.
The hand-operated sewing machine is operated by turning a wheel that drives the needle that makes the stitches, while a treadle machine is operated by having a treadle plate above the floor. As the treadle moves, it drives a rubber belt, which drives the machine and needle. These machines can only sew in straight stitches. They are straightforward machines that you operate with knobs to adjust the settings.
High-end mechanical sewing machines, like the ones on this list, come with more decorative and buttonhole stitches. Their stitches are less precise as compared to an automated one.