Business Source License (BSL)

MariaDB devised it for MaxScale in 2016. It has three dials: an Additional Use Grant spelling out what you may still do for free, a Change Date no more than four years out, and a Change License — usually GPL or Apache — that the code automatically converts to on that date. Each release starts its own clock, so there is always a fresh version that is closed and an older one that is open.

CockroachDB and Sentry adopted it in 2019. The big moment came in August 2023 when HashiCorp moved Terraform off the MPL, producing the OpenTofu fork within a month. The idea is that competitors stay at least four years behind, which in the cloud business counts as extinct.