Kernel Panic is released under an open source licenses. That means that absolutely anybody can use it, and have access to its complete source code. Open source is a very powerful approach to development that fosters distributed, collaborative development and freedom for users of the software, who can never be held to ransom by a software supplier.
There's also no hiding with open source licenses. There's no sales pitch, no marketing smokescreen, and no doubts about what you are actually getting, since the source code is 100% visible to everyone, up-front. You can get it, review it, scrutinise it and test it against your requirements and make your own decision.
Client program is licensed under GNU General Public License (GPL). GNU GPL license puts some restrictions on using code: if code is used in some project, the project's code must be open. This is important for active development of client program. At least for some time it should be unified. Maybe later some clones would appear.
On the other hand, server engine is licensed under GNU Lesser General Public License (LGPL) and is completely free of charge. The LGPL is quite a lenient license but it does come with some conditions which you should make sure you review and understand.
All the documentation for Kernel Panic is licensed under GNU Free Documentation License (FDL).