LAPACK (Linear Algebra PACKage) - Library open source containing solvers main tasks of linear algebra . Written in Fortran using another library BLAS .
There are also counterparts, maintain or even extend the functionality and provide better performance:
Intel ® MKL 
AMD ACML ™ 
Sun Performance Library 
NAG's LAPACK 
HP's mLib 
Some implementations have support for parallel execution of functions on a multiprocessor computer systems with shared memory. Analog computer with distributed memory are libraries ScaLAPACK  and PLAPACK  .
Use BSD. Surrender to eternal suckage.
I see, you can't read - everyone has forked it and closed it down. Who uses LAPACK except BSD?
Nobody uses GSL and why would you? If you're a developer (open source or not) and you want to use your own license ... would you pick GSL to do your math computations? GSL is not free. It's fine if you use GPL though.
And let's not forget other high impact libraries such as libpng (also BSDL) ...
EDIT: I'm mistaken, libpng is not BSDL.
My point is that I suspect that BSDL code (particularly when dealing with libraries) will be preferred over GPL and LGPL code ... and subsequently be more widely adopted and more widely used to solve everything from trivial to big problems.
i vote for the WTFPL licence
note this topic is not about licences, but about FSF and GNU