I'm not exactly sure what is meant by business. Commercial successful?
Anyway, here are some projects which I can recommend by its source code:
* OpenBSD. Also the other BSDs. Plan9. And the BSD tools. Linux is a bit bloated but maybe it has to be. I don't recommend the GNU tools.
* LLVM/Clang.
* WebKit. Also Chrome. Firefox not so much, although maybe it improved.
* Quake 1-3, as well as other earlier id games. Really elegant and clean. Also not that big in total. Doom 3 has become much bigger in comparison but again maybe it has to be.
* CPython. Anyway interesting also for educational purpose.
* TensorFlow. Very much not Theano.
I really enjoy reading the source code of most projects which I used at some point. Some code is nicer, some not so nice, mostly judged by how easy it is to understand and how elegant it seems to be. In any case it really is rewarding to look at it as you will gain a much better understanding of the software and often you will also learn something new.
Anyway, here are some projects which I can recommend by its source code:
* OpenBSD. Also the other BSDs. Plan9. And the BSD tools. Linux is a bit bloated but maybe it has to be. I don't recommend the GNU tools.
* LLVM/Clang.
* WebKit. Also Chrome. Firefox not so much, although maybe it improved.
* Quake 1-3, as well as other earlier id games. Really elegant and clean. Also not that big in total. Doom 3 has become much bigger in comparison but again maybe it has to be.
* CPython. Anyway interesting also for educational purpose.
* TensorFlow. Very much not Theano.
I really enjoy reading the source code of most projects which I used at some point. Some code is nicer, some not so nice, mostly judged by how easy it is to understand and how elegant it seems to be. In any case it really is rewarding to look at it as you will gain a much better understanding of the software and often you will also learn something new.