What is dual licensing?
Dual licensing is a software distribution strategy under which the same codebase is offered under two distinct licences: typically a copyleft open-source licence (e.g., GPL, AGPL) for non-commercial or community use, and a separate commercial licence for proprietary or enterprise use. Dual licensing lets vendors monetise software while preserving open-source community engagement; it requires the vendor to hold copyright (or have CLA-equivalent rights) to all contributions so it can grant both licences.
Mechanics of dual licensing
- Copyright concentration: vendor must own (or have broad CLA-assignment of) all contributions to grant proprietary licences.
- Open-source side: typically strong copyleft (GPL, AGPL) so that proprietary users cannot avoid the commercial licence by using the OSS terms in closed-source products.
- Commercial side: bespoke EULA — no copyleft obligations, optional support/SLA, indemnity, professional services.
- Trademark separation: distinct trademark policy reserves brand rights for paid version.
Famous dual-licensing examples
- MySQL (Oracle, ex-Sun/MySQL AB): GPL v2 + commercial — the canonical dual-licensing case.
- Qt (Qt Group): LGPL + commercial for proprietary integration.
- MongoDB (until SSPL pivot 2018): AGPL + commercial; later abandoned dual-licence for Server Side Public License.
- Elastic (until license change 2021): AGPL + commercial; later moved to Elastic License + SSPL.
- Sentry, Plausible, Cal.com: modern AGPL + commercial dual-licence open-core companies.
Türk açık kaynak ve commercial pratiği
Türk SaaS/yazılım şirketleri (Loops AI, Picus Security, Visma TR) dual licensing’i community/enterprise edition stratejisi olarak değerlendirebilir. Açık kaynak topluluk versiyonu KOBİ ve geliştirici benimsenmesi için, ticari versiyon kurumsal müşteri ve KVKK uyum desteği için ideal. CLA (Contributor License Agreement) yapısı Türk hukukunda telif hakkı devri çerçevesinde geçerlidir; ancak iş sözleşmesi (4857 sayılı Kanun) ile katkıda bulunan çalışanların telif haklarının açıkça düzenlenmesi gerekir.
Do: require CLA from all external contributors before merging code; clearly distinguish OSS vs. commercial features in product roadmap; monitor for licence-violation patterns in commercial use of OSS version.
Don’t: abandon copyleft licence mid-stream without community communication — MongoDB/Elastic post-relicense backlash damaged community trust.