In order to open XtratuM to all needs, we release XtratuM under a permisive licence. It is released under the GPL version 2 or above, with the explicit consideration that the code that makes use of the XtratuM services do not fall under the category of derived work.

XtratuM is released following the same licence terms that the Linux kernel. Therefore, you can develop your own proprietary applications using the licence that better fits your needs.

Please, read the GPL licence in order to avoid misunderstandings. Extracted from the GPL FAQ:

Does the GPL require that source code of modified versions be posted to the public?

The GPL does not require you to release your modified version, or any part of it. You are free to make modifications and use them privately, without ever releasing them. This applies to organizations (including companies), too; an organization can make a modified version and use it internally without ever releasing it outside the organization.

But if you release the modified version to the public in some way, the GPL requires you to make the modified source code available to the program's users, under the GPL.

Thus, the GPL gives permission to release the modified program in certain ways, and not in other ways; but the decision of whether to release it is up to you.

Does the GPL allow me to sell copies of the program for money?

Yes, the GPL allows everyone to do this. The right to sell copies is part of the definition of free software. Except in one special situation, there is no limit on what price you can charge. (The one exception is the required written offer to provide source code that must accompany binary-only release.)

Does the GPL allow me to charge a fee for downloading the program from my site?

Yes. You can charge any fee you wish for distributing a copy of the program. If you distribute binaries by download, you must provide “equivalent access” to download the source—therefore, the fee to download source may not be greater than the fee to download the binary.

XtratuM technology is based on well established hypervisor theory. We have specially avoided the use of any patented technology. There are many prior works on virtualising hardware to provide one or more isolated execution domains. There are examples of this technology as far as the IBM 360 (CP-67) that was able to run UNIX and VME on the same machine concurrently.

In any case, we (the developers) can not ensure that our code is completely free of the patent problems. In fact we think that software patents is an awful idea that only benefits big companies and lawyers, and compromises scientific advance. Society as a whole is the big looser of the software patent system.

The number of registered patents is larger than 50000. Can someone (but Donald Knuth) prove that a new idea has not been already patented in some incarnation? We have seen several patents that claim to patent the same thing with so sligthly differences that it is harder to know which are the diferences between them than to understand the basic patented idea.

All XtratuM code has been completely written by us.