1.
sole practitioner
2. a sole trader
If you’re a sole trader, you run your own business as an individual and are self-employed. You can take on staff - being a sole trader means you’re responsible for the business, not that you have to work alone.
3. single member company
4. sole partnership
5. freelancer
In 1872 the artist left the academy and worked as a freelancer.
I'm a freelancer doing translations for various companies.