Hi Rodrigo,
I am not familiar with LibreS3 but if it uses the standard S3 API there is a good chance JetS3t will work with it.
To use a different service endpoint set the "s3service.s3-endpoint" and related properties in your project's jets3t.properties file, or the JetS3tProperties object you provide when you create a service instance. Some services also require you to set an alternative URL path prefix, which you can do with the "s3service.s3-endpoint-virtual-path" property.
Hope this helps, and let us know how it goes.
Regards,
James