Free but non-free?
The software that run Fossbill is Free as in Freedom, and can easily run on any personal machine, or micro-servers. We will name any Fossbill server as instance here.
The fossbill.org instance is non-free, meaning that it require a payment subscription to be used. There is a 7 day grace period that allow the user to test the service for some time. After the grace period, it become impossible to generate new bills or quotes. But it stay possible to browse any user data already present on the service.
Fossbill choose a non-free business plan to make sure that the users that actually use the service are our final customers. As a service subscriber, you are the only person we are accountable for.