No, not Open Source, which rather makes my point. The Open Source Definition explicitly forbids restrictions on commercial use ('No Discrimination Against Fields of Endeavor'). The developers claim there are 'many definitions' of Open Source, which isn't correct for software, and the current version of the Wikipedia page they link to doesn't support this claim. This is not the main problem with the LinuxSampler licence, however. Instead of writing their own licence, they've added a restriction to the GPL, which isn't allowed if you still want to call it the GPL. This means that their licence contradicts itself, which is one reason why you won't find Linuxsampler in (say) Debian non-free. The developers are of course perfectly free to distribute their software for non-commercial use only, but they just haven't gone about it in the right way. They should just drop the 'Open Source' claim and come up with their own licence (which could be based on the GPL, but should not include the preamble, GPL branding, or anything else that conflicts with their non-commercial clause).