The Stockfish engine was developed by Tord Romstad, Marco Costalba, and Joona Kiiski. It is now being developed and maintained by the Stockfish community.
The Stockfish project started with the open source Glaurung engine, authored by Tord Romstad. In November 2008, Marco Costalba forked the Glaurung 2.1 code and introduced Stockfish 1.0. Tord and Joona Kiiski joined the Stockfish project and the Glaurung project slowly faded away. Meanwhile, Stockfish quickly rose to become the strongest open source chess engine, with frequent updates every few months. Today, it remains one of the strongest engines in the world.
About this website
About the GPL
Stockfish is free, and distributed under the GNU General Public License version 3 (GPL v3). Essentially, this means you are free to do almost exactly what you want with the program, including distributing it among your friends, making it available for download from your website, selling it (either by itself or as part of some bigger software package), or using it as the starting point for a software project of your own.
The only real limitation is that whenever you distribute Stockfish in some way, you MUST always include the full source code, or a pointer to where the source code can be found, to generate the exact binary you are distributing. If you make any changes to the source code, these changes must also be made available under the GPL.
For full details, read the license file.