much of the software maemo is based on is GPL, but there are some parts that are closed source (the maemo 4 network manager for instance).

the trademark of maemo however is another matter. You cant just up and slap the open parts of maemo on some random device and call it a maemo device, unless nokia say its ok. Thats why the only companies that claim to be using maemo on their products outside of nokia, is operating in china.

much more of this will be opened now that one go from maemo to meego, thanks to projects like ofono and connman.