Historical Permission Notice and Disclaimer
The Historical Permission Notice and Disclaimer is an open source license, approved by the Open Source Initiative and verified as GPL-compatible by the Free Software Foundation. It is unique among the OSI's licenses because of the choices it allows in its construction; it lets the licensor pick anywhere from 0-2 warranty disclaimers, whether they want to prohibit the author's name from being used in publicity or advertising surrounding a distribution, and other spelling and grammar options. Besides this, the license can be almost functionally identical to the new 3-clause BSD License, or the MIT License.
Variants of this license are in use primarily in older software, including the original BSD kernel. Today, it is most popular to choose either the new 3-clause BSD License or the MIT License to meet the licensing needs of the developer.
This is the only OSI-certified license that can lack a disclaimer of warranty.