I hold the view that it is beneficial for scientists to share their ideas and techniques freely.
Recently I wrote an opinion piece on Open Source and CFD, entitled
Science and fluid dynamics should have more open sources
It describes in about 8 pages why scientists are reluctant to let others see their code. The intended audience is academics like me, who write medium size research software and collaborate with a small group of graduate students as well as a few collaborators in other universities or companies. I try to provide an explanation based on the different ways in which academics and programmers gain reputation. I then advise a change of minds: science should be more open.
I have distributed under the GPL some of my work with Daniel Rothman on Lattice Gas Cellular Automata (see lattice gases ) .
My work with my colleagues and students on droplets and bubbles led to two codes, Surfer written by myself, Gianluigi Zanetti, Ruben Scardovelli, Jie Li, Denis Gueyffier and others, and Gerris, written by Stephane Popinet.