Earlier quoted context omitted.
You offer a copyleft license like AGPL but also offer a paid license for those who don't want to deal with AGPL. Since you as the creator own the copyright, you can license it however you want, including multiple licenses simultaneously.
Forgive me for a naive question but how do external contributions to the AGPL code find their way back to the commercially licenced code? Are all contributions to the "original" pre-licenced source? If so is there some extra legalese to ensure that the changes will always end up in the AGPL source too? I know of many successful projects using dual licencing so it must work, I'm just wondering how on a legal front.
- Agree to a Contributor License Agreement that grants the project owner an irrevocable world-wide commercial license (probably missing a few adjectives but you get the idea)
- Transfer the copyright
- Release to public domain