LedgerSMB is being made available under the terms of the GNU Public License version 2, or shorter GPLv2 11http://www.opensource.org/licenses/GPL-2.0.
The project attaches this meaning to the license: The copyright holders grant you the right to copy and redistribute the software. In case you make any modifications to the sofware you’re obligated to make public those changes. You are however, free to use the APIs from your own software without being required to publish your own software.
The project considers the following to be APIs:
URLs with their input and output
Webservices of any kind
Function and object calls
The effect of this interpretation is that changes directly to the code base as well as inheritance of classes defined in the software constitute ”making modifications”.