The XFree86 Project's basic licensing philosophy has always been summed up as "You can do what you like with the code except claim you wrote it." Expressed more formally, it means that the licenses acceptable for code that makes up XFree86 must meet the following conditions:
A range of Open Source and Free Software licenses meet these conditions. The licenses in this document are examples of acceptable licenses. Contributors to XFree86 are encouraged to choose the license type that best suits them. If you have any questions about whether a specific license fits in with the XFree86 licensing policy, please contact us.