The group behind the world's most popular smartphone operating system - Symbian - is giving away "billions of dollars" worth of code for free.
The Symbian Foundation's decision to make its code open source means that any organisation or individual can now use and modify it "for any purpose".
Symbian has shipped in more than 330m mobile phones, the foundation says.
It believes the move will attract new developers to work on the system and help speed up the pace of improvements.
"This is the largest open source migration effort ever," Lee Williams of the Symbian Foundation told BBC News.
"It will increase rate of evolution and increase the rate of innovation of the platform."
Ian Fogg, principal analyst at Forrester research, said the move was about Symbian "transitioning from one business model to another" as well as trying to gain "momentum and mindshare" for software that had been overshadowed by the release of Apple's iPhone and Google Android operating system.