There's a converter program that outputs, AFAIK basically the same .brd file, but in ASCII rather than binary format. (Go figure that manufacturers won't share their binary formats, and go out of their way to grudgingly make ASCII formats for customer-demanded interoperability, even though it's all the same to a computer.)
I once looked into it and it might be possible to obtain the converter programs from a free download, but it's not obvious if they are usable alone, or if even those simple apps need the dreaded license manager service running. And, for that matter, if such behavior is easily patched out (*cough*), or what. That particular job ended up going to a subcontractor to do the file conversion for us (they have practically everything, while we only have Altium).
Tim