This source code has two packages with different licenses:
In both cases any modification of the source code must be provided to the users, and it will be highly appreciated if contributed back to rtpmidid.
But the LGPL 2.1+ allows to be used as library of free or commercial software.
Any modification of the daemon itself must provide accompaning source code.
The source code of the directories include and lib is under LGPL2.
This allows to reuse the library on any software you see fit.
The source code of the directory src is under GPLv3.