Ok, that I shall remember. Thank you.
I am not trying to make money by making a derivative product. Just searching for a file hosting service that will not force me to use closed-source client run on my completely open source Fedora PC (no, it doesn't have flash and I don't need it!)
Some services are very strict on hosting non-GPL products and that's why I asked. They can work with standard CVS or equivalent open source products and so no need for a closed-source who-knows-what-it-does client.
If all else fails I shall use a Windows PC to run the client but my development shall stay on the Linux system.