MIT License - Various Versions

Various Versions

Because MIT has used many licenses for software, "MIT License" is considered ambiguous by the Free Software Foundation. "MIT License" may refer to the "Expat License" (used for Expat) or to the "X11 License" (also called "MIT/X Consortium License"; used for the X Window System by the MIT X Consortium). The "MIT License" published on the official site of Open Source Initiative is the same as the "Expat License".

Compared to the Expat License, the X11 License and the "MIT License" chosen in 1998 for ncurses by the Free Software Foundation add this clause:

Except as contained in this notice, the name(s) of the above copyright holders shall not be used in advertising or otherwise to promote the sale, use or other dealings in this Software without prior written authorization.

The XFree86 Project uses a modified MIT License for XFree86 version 4.4 onward. The license includes a clause that requires attribution in software documentation, like the original 4-clause BSD license. The Free Software Foundation contends that this addition is incompatible with the version 2 of the GPL, but compatible with version 3:

The end-user documentation included with the redistribution, if any, must include the following acknowledgment: "This product includes software developed by The XFree86 Project, Inc (http://www.xfree86.org/) and its contributors", in the same place and form as other third-party acknowledgments. Alternatively, this acknowledgment may appear in the software itself, in the same form and location as other such third-party acknowledgments.