BoxBilling is a licensed solution that you can get on the software editor website.
To activate the product, you'll need a license. There are two options for the license: A free license for small company and a monthly-billed license for medium to large sized company. The advantage of the paying version, beside not limiting the number of staff, allowing more currencies than euros and US dollars, is the possibility to use BoxBilling as a white-label product.
For more informations, see the website:
To install the software you can follow the instruction of the BoxBilling manuel: