Simplify the following text for a Grade 14 native English-speaking person.
Original: While other copyright holders of other software systems used the GPL as their license , FSF was the only organization to regularly assert its copyright interests on software licensed under the GPL until Harald Welte created gpl-violations .
Simplified: While other copyright holders of other software systems adopted the GPL as their license , FSF was the only organization to regularly assert its copyright interests on software so licensed until Harald Welte launched gpl-violations .