Topic summary
GPLv2
Extracted from the Wikipedia article GNU General Public License.
Version 3
GPLv3 improved compatibility with several free software licenses, such as the Apache License (version 2.0) and the GNU Affero General Public License (which GPLv2 could not be combined with). However, GPLv3 software could be combined with and share code with GPLv2 software only if two conditions were met: the GPLv2 license that was used contained the optional "or later" clause, and the software was upgraded to GPLv3. While the "GPLv2 or any later version" clause is considered by FSF to be the most common form of licensing GPLv2 software, Toybox developer Rob Landley described it as a lifeboat clause. Software projects licensed with the optional "or later" clause include Joomla and the GNU Project, while a prominent example without this clause is the Linux kernel.