> Can (e.g) Postgresql wait until the whole world is relying on their software, and then pull a licence change that makes it non-free/libre and requiring a paid

> Can (e.g) Postgresql wait until the whole world is relying on their software, and then pull a licence change that makes it non-free/libre and requiring a paid licence fee? It's happened before: https://en.wikipedia.org/wiki/Contributor_License_Agreement#Relicensing_controversy https://en.wikipedia.org/wiki/Contributor_License_Agreement#... The short version is that if you hold the copyright, you can relicense new versions as you see fit, but can't change the license on already released versions. If the copyright is held by individual contributors, then you'd need unanimous consent from all of them, because the company is effectively licensing it from them in approximately the same way a user would. PostgreSQL, specifically, is in the latter category, so it's not really a concern: https://wiki.postgresql.org/wiki/Developer_FAQ#Do_I_need_to_sign_a_copyright_assignment.3F https://wiki.postgresql.org/wiki/Developer_FAQ#Do_I_need_to_...