The GPL itself offers no such option, but if the copyright holder(s) choose to they may offer whatever alternatives they choose. Many significant open source a

The GPL itself offers no such option, but if the copyright holder(s) choose to they may offer whatever alternatives they choose. Many significant open source applications are offered under this model such as MySQL. The catch is that the more copyright holders there are the more likely it is that someone who has contributed a non-trivial part of the project will not agree, in which case their work would have to be removed/replaced to allow for relicensing. Large projects that have not required a CLA from contributors are effectively impossible to relicense.