|Publisher||2005, Lawrence Rosen|
|SPDX identifier||OSL-1.0, OSL-1.1, OSL-2.0, OSL-2.1, OSL-3.0|
The Open Software License (OSL) is a software license created by Lawrence Rosen. The Open Source Initiative (OSI) has certified it as an open-source license, but the Debian project judged version 1.1 to be incompatible with the DFSG. The OSL is a copyleft license, with a termination clause triggered by filing a lawsuit alleging patent infringement.
Many people in the free software / open-source community feel that software patents are harmful to software, and are particularly harmful to open-source software. The OSL attempts to counteract that by creating a pool of software which a user can use if that user does not harm it by attacking it with a patent lawsuit.
The OSL has a termination clause intended to dissuade users from filing patent infringement lawsuits:
Another goal of the OSL is to warrant provenance.
OSL explicitly states that its provisions cover derivative works even when they are distributed only through online applications:
The OSL is intended to be similar to the LGPL. Note that the definition of Derivative Works in the OSL does not cover linking to OSL software/libraries so software that merely links to OSL software is not subject to the OSL license.
The OSL is not compatible with the GPL. It has been claimed that the OSL is intended to be legally stronger than the GPL (with the main difference "making the software available for use over the Internet requires making the source code available" that is the same goal as the even newer Affero General Public License (AGPL), that is compatible with GPLv3), however, unlike the GPL, the OSL has never been tested in court and is not widely used.
The restriction contained in Section 9 of the OSL reads:
If You distribute or communicate copies of the Original Work or a Derivative Work, You must make a reasonable effort under the circumstances to obtain the express assent of recipients to the terms of this License.
In its analysis of the OSL the Free Software Foundation claims that "this requirement means that distributing OSL software on ordinary FTP sites, sending patches to ordinary mailing lists, or storing the software in an ordinary version control system, can arguably be a violation of the license and would subject violators to possible termination of the license. Thus, the OSL makes it challenging to develop software using the ordinary tools of Free Software development."
If the FSF claim is true then the main difference between the GPL and OSL concerns possible restrictions on redistribution. Both licenses impose a kind of reciprocity condition requiring authors of extensions to the software to license those extensions with the respective license of the original work.
The patent action termination clause, described above, is a further significant difference between the OSL and GPL.
It is optional, though common for the copyright holder to add “or any later version” to the distribution terms in order to allow distribution under future versions of the license. This term is not directly mentioned in the OSL. However, it would seem to violate section 16, which requires a verbatim copy of the license.