Professional Server license is valid for any individual, company or organization (both for-profit and non-profit) requiring the software for general commercial use or for non-commercial purposes.
Professional Server license grants you rights to:
If you require more than three Build Agents for a single Professional Server instance, you can purchase additional Build Agents for $299 per agent.
Alternatively, you may want to consider buying Enterprise Server license, which removes all the restrictions of the Professional license. Enterprise Server license is available for purchase at the price of $1999.
Learn more about the differences between the Professional and the Enterprise Server licenses.