Ask Slashdot: What Is The Best Place To Suggest A New Open Source Software?

dryriver writes: Somebody I know has been searching up and down the internet for an open source software that can apply GPU pixel shaders (HLSL/GLSL/Cg/SweetFX) to a video and save the result out to a video file. He came up with nothing. So I said "Why not petition the open source community to create such a tool?" His reply was "Where exactly does one go to ask for a new open source software?" So that is my question: Where on the internet can one best go to request that a new open source software tool that does not exist yet be developed? Or do open source tools only come into existence when someone — a coder — starts to build a software, opens the source, and invites other coders to join the fray?