Hi, sorry if this is a stupid question but i want to be 100%, if an API is open source, such as the following http://www.portaudio.com/ and http://bulletphysics.org/wordpress/, does this mean that if i created a game using their software and made a bit of money off it i wouldn't be liable to get sued by them?
In general, no. Open source as such does not imply that you can use it any way you want, without limits or obligations. Some open source licenses are very liberal, others are not.
In the case of the two libraries you mentioned, the answer is howerver: yes (read the licenses, they explicitly say so).
(Also, since you said "API", maybe unintentionally, note that an API and an implementation or a library are not necessarily the same or under the same license.)
The GPL and certain other licenses are viral, infecting other source code that derives or uses GPL licensed code.
Other licenses such as apache and creative commons attribution are much more permissive.
Do your research before including open source code and you'll be fine.
Always respect open source and other licenses. Just because you haven't paid for it, it doesn't mean it has no value and someone poured weeks or months or even years of their life into it and that deserves to be respected IMHO.
Licnesing is complex. You are best off asking a lawyer. That said, Open Source has a few different models.
Permissive: Software that has a license like the MIT, BSD, X, etc. allows you to use the library however you wish. They will perhaps have a few documentation requirements, such as giving them credit, noting that the original library was under its license, or that you not use the authors' name to advertise your product. It's generally then just a good idea to list all such libraries you use in your credits, with their license. Again, though, ask a lawyer for safety.
Free Software: This kind of software, usually covered by the GPL, is "viral." If you use it, your entire application must be released under a similar license. Note that you are still completely allowed to charge for copies of the software or for consulting services regarding the software, but you can't legally stop your customers from giving away the software for free on their own because the license gives them that right. Again, though, ask a lawyer for safety.
Free Software with Dynamic Linking Exception: This is software covered by the LGPL for the most part. Such software only applies the Free Software restriction to a DLL containing the software. You can keep your Executable application or other libraries under whatever license you want. If you modify the software that goes into the DLL, you must share those modifications freely under the same license, but that's it. Plenty of commercial closed-source applications use LGPL DLLs, though it's usually a bit of a legal minefield. Again, though, ask a lawyer for safety.
Non-commercial: Such software is technically-speaking not "Open Source" in the official OSI definition because it discriminates against a class of users (commercial retailers). However, this is a category of software that exists, both when the source is freely available and for software without source access. A lawyer can't get you out of such a license, but you should check with a lawyer anyway to make sure you aren't accidentally using software with a non-commercial licensing clause.
Other: There are a bazillion other licenses. A license that looks like it might be a Permissive license might not actually be as permissive as you think, so... again, ask a lawyer for safety.
Note that a lot of companies, even when they are relatively certain that they are using the library legally, like to sign a contract with the library author under a nominal fee just to be sure. Keeping in mind that works are automatically copyrighted upon release whether the author wants it or not, and that most of the various Open Source and Free Software licenses are relatively untested in court, corporate lawyers are often unwilling to "risk" assuming that the permissions granted by such licenses can't be revoked by the author without a firm contract that the author will not do so.
The moral of this story is that US and Worldwide copyright laws are balls and built by lawyers to be overly complex to ensure that you have to pay said lawyers heaps of money in order to safely release even the simplest of products. :/
Sean Middleditch – Game Systems Engineer – Join my team!
