Freeware per definition means Software you are free to use, sometimes only when certain conditions are met (private, noncommercial use). You are not allowed to get the source and modify it.
Of course is open software free, but not 'free like freeware', it is 'free as in freedom'. The source is available and you are able to use it both privately and commercially. But the most important point of the GPL is, you may modify it but must redistribute it under the GPL and provide the source.